Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 18 Oct 2009
Posts: 48
Schools: Kellogg

If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
25 Oct 2009, 02:41
Question Stats:
46% (02:24) correct 54% (02:42) wrong based on 318 sessions
HideShow timer Statistics
If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have? A. 60 B. 120 C. 240 D. 275 E. 300
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
GMAT Strategies: http://gmatclub.com/forum/slingfoxsgmatstrategiescondensed96483.html




Math Expert
Joined: 02 Sep 2009
Posts: 47112

Re: Feeding the Chickens
[#permalink]
Show Tags
25 Oct 2009, 12:35
slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\) \(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics




Director
Joined: 23 Apr 2010
Posts: 555

Re: Feeding the Chickens
[#permalink]
Show Tags
06 Dec 2010, 06:34
Bunuel, I have tried a different approach. Can you please explain why it didn't work? Thank you.
x ... number of chickens k ... 1 chicken consumption per day T ... total number of days for x chickens to live given their current number
We get the following equations:
(y  75)/k = T +20 (y + 100)/k = T  15 y/k = T
However, I couldn't solve the equations. I got k = 5. But substituting 5 into the equation, I couldn't solve it.
Thank you.



GMAT Club Legend
Joined: 16 Oct 2010
Posts: 8128
Location: Pune, India

Re: Feeding the Chickens
[#permalink]
Show Tags
06 Dec 2010, 09:03
slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 or you can make your equations in this way: Let us say he has planned for d days for c chickens. According to the question, the food 75 chicken consumed in d days will last 20 days if consumed by (c  75) chickens So 75d = (c  75)20 ..... (I) What c chickens consumed in 15 days, 100 chickens will consume in (d  15) days 15c = 100(d  15) ......(II) Solve I and II to get c = 300
_________________
Karishma Private Tutor for GMAT Contact: bansal.karishma@gmail.com



Manager
Status: Joining Cranfield Sep 2014
Joined: 01 Sep 2012
Posts: 59
Concentration: Technology, General Management
GMAT 1: 530 Q50 V14 GMAT 2: 630 Q48 V29
WE: Engineering (Energy and Utilities)

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
19 Oct 2013, 05:42
bumpbot wrote: Hello from the GMAT Club BumpBot!
Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos).
Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. Let Number of Chickens be X The number of days chicken will eat a fixed stock will be inversely proportional to number of chickens. Hence if number of days X chicken will eat the stock will be D = K/ X If number of chicken is reduced by 75 then D+20 = K / (X75) If number of chicken is increaded by 100 then D15 = K / (X+100) Replacing D=K/X in above two equations: K/X + 20 = K / (X75) K/X  15 = k / (X+100) solving above two equations gives X =300. Answer is E



Intern
Joined: 10 Oct 2013
Posts: 18
Location: India
Concentration: International Business, Technology
GMAT 1: 620 Q39 V35 GMAT 2: 710 Q47 V40
WE: Sales (Computer Hardware)

Re: Feeding the Chickens
[#permalink]
Show Tags
02 Nov 2013, 10:41
Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\) \(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. Thank you for the explanation Bunuel. However, I do not understand something here: How does multiplying the number of days (d) with the number of chickens (x) give the amount of feed the farmer has ? Shouldn't it rather be the amount of feed the chickens consume in one d days ?



Math Expert
Joined: 02 Sep 2009
Posts: 47112

Re: Feeding the Chickens
[#permalink]
Show Tags
03 Nov 2013, 11:39
nishantsharma87 wrote: Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\) \(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. Thank you for the explanation Bunuel. However, I do not understand something here: How does multiplying the number of days (d) with the number of chickens (x) give the amount of feed the farmer has ? Shouldn't it rather be the amount of feed the chickens consume in one d days ? That's because the amount of feed each chicken eats a day, say z, can be reduced on both sides: \(zxd=z(x75)(d+20)\) > \(xd=(x75)(d+20)\); \(zxd=z(x+100)(d15)\) > \(xd=(x+100)(d15)\). Hope it's clear.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 10 Oct 2013
Posts: 18
Location: India
Concentration: International Business, Technology
GMAT 1: 620 Q39 V35 GMAT 2: 710 Q47 V40
WE: Sales (Computer Hardware)

Re: Feeding the Chickens
[#permalink]
Show Tags
04 Nov 2013, 11:07
Thank you for the explanation as always Bunuel!
I find such word problems, where we have to assume some constants/variable to solve the question (that cancel out before the final solution arrives) and ALSO infer its relationship with the variables/constants given in the word problem, quite tricky (specially WORK/RATE problems! )
It'll be very helpful if you can provide some similar questions or content (or their link) to practice.
Cheers!



Manager
Joined: 10 Mar 2013
Posts: 236
GMAT 1: 620 Q44 V31 GMAT 2: 690 Q47 V37 GMAT 3: 610 Q47 V28 GMAT 4: 700 Q50 V34 GMAT 5: 700 Q49 V36 GMAT 6: 690 Q48 V35 GMAT 7: 750 Q49 V42 GMAT 8: 730 Q50 V39

Re: Feeding the Chickens
[#permalink]
Show Tags
29 Dec 2013, 19:58
Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\) \(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. Wow! When I first saw this question, I had no clue even how to begin. Bunuel, where in the problem suggests that one should take this approach?



Retired Moderator
Joined: 16 Jun 2012
Posts: 1076
Location: United States

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
30 Dec 2013, 04:11
slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 This question is similar to workrate questions. The key is always calculate how much work each person/machine does in 1 unit of time. For this question, we have: number of chickens = X stock feed = T (days) It means X chickens can be fed in T days > 1 chicken eats in 1 day = 1/(XT)1st scenario, we sell 75 chickens, we havenumber of chickens = X  75 stock feed = T + 20 (days) > 1 chicken eats 1 day = 1/[(X75)(T+20)] Because the amount of food each chicken eats in 1 day is the same:> 1/XT = 1/[(X75)(T+20)] > XT = XT+ 20X  75T  1500 > 20X  75T  1500 = 02nd scenario: we buy 100 chickensnumber of chickens = X + 100 stock feed = T  15 (days) > 1 chicken eats 1 day = 1/[(X+100)(T15)] Because the amount of food each chicken eats in 1 day is the same:> 1/XT = 1/[(X+100)(T15)] > XT = XT 15X +100T  1500 > 15X +100T  1500 = 0Solve 2 equations 20X  75T  1500 = 0 15X +100T  1500 = 0Clearly, X = 300 Hence, E is correct. We have
_________________
Please +1 KUDO if my post helps. Thank you.
"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."
Chris Bangle  Former BMW Chief of Design.



SVP
Joined: 06 Sep 2013
Posts: 1869
Concentration: Finance

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
18 Feb 2014, 16:50
Its quite a journey but here we go. (q75)(t+20) and (q+100)(t15). Now we need to equal each to qt. So we will have 20q  75t  75(20) on the first equation and 15q + 100t  100(15) on the second equation. We could simplify some terms but the point is we need to find 'q' so anyways after simplifying we can multiply the first equation by 3 and we're left with 12q  60t 75 *(4) *(4) and multiply the second by 3 to get 9q + 60t  100 (3)*3. So then we finally get to 3q = 900, q = 300
E is the answer
If any one comes up with a fast way to do this I'll def provide some Kudos Cheers! J



Intern
Joined: 24 Jun 2015
Posts: 46

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
10 Jul 2015, 07:03
nonameee wrote: Bunuel, I have tried a different approach. Can you please explain why it didn't work? Thank you.
x ... number of chickens k ... 1 chicken consumption per day T ... total number of days for x chickens to live given their current number
We get the following equations:
(y  75)/k = T +20 (y + 100)/k = T  15 y/k = T
However, I couldn't solve the equations. I got k = 5. But substituting 5 into the equation, I couldn't solve it.
Thank you. Hi, I also did the problem the same way and could not solve it, does somebody can help us to know why is this approach incorrect? Thanks a lot BunuelLuis Navarro Looking for 700



Current Student
Joined: 20 Mar 2014
Posts: 2641
Concentration: Finance, Strategy
GPA: 3.7
WE: Engineering (Aerospace and Defense)

If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
10 Jul 2015, 09:27
luisnavarro wrote: nonameee wrote: Bunuel, I have tried a different approach. Can you please explain why it didn't work? Thank you.
x ... number of chickens k ... 1 chicken consumption per day T ... total number of days for x chickens to live given their current number
We get the following equations:
(y  75)/k = T +20 (y + 100)/k = T  15 y/k = T
However, I couldn't solve the equations. I got k = 5. But substituting 5 into the equation, I couldn't solve it.
Thank you. Hi, I also did the problem the same way and could not solve it, does somebody can help us to know why is this approach incorrect? Thanks a lot BunuelLuis Navarro Looking for 700 Couple of things here: I am assuming x=y as nowhere y is defined . Also if I solve the 3 equations, (y  75)/k = T +20 (y + 100)/k = T  15 y/k = T I will get k=5. As feed/day can not be a negative number, this clearly shows that something is wrong with this approach. It was mentioned earlier that, x ... number of chickens k ... 1 chicken consumption per dayT ... total number of days for x chickens to live given their current number How can you get #days by dividing (y75) by k in equation 1? You will get a quantity that will be [# of chickens * 1 chicken consu/ day]. This is not the number of days that you equate to in (y  75)/k = T +20. For getting number of days the desired quantity should be [some unit *( day / some unit)]. The easiest way is to take the quantity that is not changing = the total feed with the farmer. Then proceed with this information as Bunuel has shown above. From my personal experience, in word problems, whenever there is a 'constant'quantity, it is better to use that to get the other values.



VP
Joined: 07 Dec 2014
Posts: 1036

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
18 Sep 2017, 20:15
slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 total difference between chickens bought and sold=100(75)=175 total difference between available feed days=20(15)=35 175/35=5/1 ratio between number of chickens and available feed days let c=current number of chickens c/5=available feed days c*c/5=(c75)(c/5+20) c=300 chickens E



Manager
Joined: 06 Oct 2015
Posts: 85

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
22 Sep 2017, 06:07
Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\)\(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. How have you got the colored part?



Math Expert
Joined: 02 Sep 2009
Posts: 47112

If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
22 Sep 2017, 06:13
NaeemHasan wrote: Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\)\(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. How have you got the colored part? \(\frac{d+20}{d15}=\frac{x+100}{x75}\); Crossmultiply: \((d+20)(x75)=(x+100)(d15)\); Expand: \(dx 75d + 20x  1500=dx15x+100d1500\); Cancel dx and 1500, and rearrange: \(35x=175d\); Reduce by 5: \(x =5d\). Hope it's clear.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 29 Sep 2017
Posts: 6

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
23 Oct 2017, 10:55
Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\) \(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. can you please explain why x=5d? i got 5d=25 x, so x=1/5d thanks so much.



Math Expert
Joined: 02 Sep 2009
Posts: 47112

Re: If the farmer sells 75 of his chickens, his stock of feed
[#permalink]
Show Tags
24 Oct 2017, 00:37
ayas7 wrote: Bunuel wrote: slingfox wrote: If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned, but if he buys 100 more chickens, he will run out of feed 15 days earlier than planned. If no chickens are sold or bought, the farmer will be exactly on schedule. How many chickens does the farmer have?
A. 60 B. 120 C. 240 D. 275 E. 300 # of chickens  x # of days  d If the farmer sells 75 of his chickens, his stock of feed will last for 20 more days than planned > Amount of feed equals \(xd=(x75)(d+20)\); If he buys 100 more chickens, he will run out of feed 15 days earlier than planned > Amount of feed equals \(xd=(x+100)(d15)\). \((x75)(d+20)=(x+100)(d15)\) > \(\frac{d+20}{d15}=\frac{x+100}{x75}\) > \(x=5d\) \(xd=(x75)(d+20)\) > \(5d^2=(5d75)(d+20)\) > \(d^2=(d15)(d+20)\) > \(d=60\) > \(x=5d=300\). Answer: E (300) Hope it helps. can you please explain why x=5d? i got 5d=25 x, so x=1/5d thanks so much. \((x75)(d+20)=(x+100)(d15)\) Expand: \(xd +20x75d1500=xd15x+100d1500\); Rearrange and cancel xd and 1500: \(35x=175d\); Reduce by 35: \(x=5d\).
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics




Re: If the farmer sells 75 of his chickens, his stock of feed &nbs
[#permalink]
24 Oct 2017, 00:37






