Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 15 Oct 2009
Posts: 11

The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
Updated on: 28 Mar 2012, 09:08
Question Stats:
75% (02:09) correct 25% (02:27) wrong based on 959 sessions
HideShow timer Statistics
The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A? A. 8 B. 9 C. 10 D. 11 E. 12
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by changhiskhan on 03 Apr 2010, 12:57.
Last edited by Bunuel on 28 Mar 2012, 09:08, edited 1 time in total.
Edited the question and added the OA




Math Expert
Joined: 02 Sep 2009
Posts: 47924

Re: Help with a ratio question.
[#permalink]
Show Tags
28 Mar 2012, 10:09
imhimanshu wrote: Hey Bunuel, While giving test, I have been able to solve it correctly using back solving. However, when I revisited this question, I was unable to solve it at the first go. Request you to help me out.. Let the multiplier be x for Class A . Therefore, number of boys: 3x and number of girls 4x Let the multiplier be y for Class B. Therefor, number of boys: 4y and number of girls : 5y It is given that  3x= 4y+1 (A) and 4x=5y+2 (B) Also As per question: 3x+4y/4x+5y = 17/22 (combined boys: combined girls) (C) Putting the value from A and B in Equation C giving me weird results  y is coming out to be 6/13 I have also gone through the replies posted above and I am not too sure that I would be able to ignore the superfluous statement in the real time exam... so hoping to see the solution utilizing the info. Thanks H This problem is a rare example of a question which provides redundant information: we CAN solve the question without knowing that the ratio of boys to girls in the combined class is 17 to 22. The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A? A. 8 B. 9 C. 10 D. 11 E. 12 The ration of boys to girls in Class A is 3 to 4: # of boys is 3x and # of girls is 4x, for some positive integer multiple x; The ration of boys to girls in Class B is 4 to 5: # of boys is 4y and # of girls is 5y, for some positive integer multiple y; Class A has one more boy and two more girls than class B: 3x=4y+1 and 4x=5y+2. Now, we have the system of two distinct linear equations with two unknowns, which means that we can solve it. Solving for x we get x=3. Since # of girls in Class A is 4x the there are 4*3=12 girls. Answer: E. So, as you can see you've done everything right, you just should have solved the system of equations rather than applying some kind of substitution. 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




CEO
Status: Nothing comes easy: neither do I want.
Joined: 12 Oct 2009
Posts: 2653
Location: Malaysia
Concentration: Technology, Entrepreneurship
GMAT 1: 670 Q49 V31 GMAT 2: 710 Q50 V35

Re: Help with a ratio question.
[#permalink]
Show Tags
03 Apr 2010, 13:42
IMO E 12 Let for Class A boys = x and girls = y then for class B boys = x1 and girls = y1 x/y = 3/4 and (x1)/(y2) = 4/5 put the value of x in second equation we get y =12 another way.. since x = 3/4 * y that means y must be multiple of 4 ( because x must be an integer) so the only possibilities are 8 and 12...for y = 8 and 12 we get x as 6 and 9 substitute in 2nd equation to satisfy..... (x1)/(y2) = (61)/(82) is not equal to 4/5 thus ans is 12.
_________________
Fight for your dreams :For all those who fear from Verbal lets give it a fight
Money Saved is the Money Earned
Jo Bole So Nihaal , Sat Shri Akaal
Support GMAT Club by putting a GMAT Club badge on your blog/Facebook
GMAT Club Premium Membership  big benefits and savings
Gmat test review : http://gmatclub.com/forum/670to710alongjourneywithoutdestinationstillhappy141642.html




Manager
Joined: 04 Apr 2010
Posts: 88
Schools: UCLA Anderson

Re: Help with a ratio question.
[#permalink]
Show Tags
05 Apr 2010, 17:17
gurpreetsingh gives a good algebraic explanation. This question is also easy to solve by using multiples of the original ratios. We can set up the ratios Ba (boys in A) to Ga (girls in a), and Bb (boys in b) to Gb (girls in B). Ba/Ga = 3/4 Bb/Gb = 4/5 When combined, we'd like our final ratio ratio to be 17/22. If you write out a few multiples of each of the original ratios, Ba/Ga = 3/4, 6/8, 9/12... Bb/Gb = 4/5, 8/10, 12/15... It's easy to see that by picking 9/12 for A and 8/10 for B will give you a combined ratio of 17/22. Thus, we will have 12 girls in group A. Answer: E
_________________
If this post was helpful, please give Kudos.



Manager
Joined: 07 Jan 2010
Posts: 209

Re: Help with a ratio question.
[#permalink]
Show Tags
10 Apr 2010, 04:24
good question... first I got stuck with big equation ...then applied the short used by gurpreet also...once you figure out it has to be between 8 and 12, it becomes easier.
E it is.



Intern
Joined: 16 Jul 2010
Posts: 10

Re: Help with a ratio question.
[#permalink]
Show Tags
09 Oct 2010, 19:04
I understand gurpreetsingh's algebraic explanation, but does that mean that the 17/22 ratio is superfluous? I'm not used to seeing extra info on GMAT questions.



Senior Manager
Joined: 07 Sep 2010
Posts: 288

Re: Help with a ratio question.
[#permalink]
Show Tags
28 Mar 2012, 07:10
Hey Bunuel, While giving test, I have been able to solve it correctly using back solving. However, when I revisited this question, I was unable to solve it at the first go. Request you to help me out.. Let the multiplier be x for Class A . Therefore, number of boys: 3x and number of girls 4x Let the multiplier be y for Class B. Therefor, number of boys: 4y and number of girls : 5y It is given that  3x= 4y+1 (A) and 4x=5y+2 (B) Also As per question: 3x+4y/4x+5y = 17/22 (combined boys: combined girls) (C) Putting the value from A and B in Equation C giving me weird results  y is coming out to be 6/13 I have also gone through the replies posted above and I am not too sure that I would be able to ignore the superfluous statement in the real time exam... so hoping to see the solution utilizing the info. Thanks H



Manager
Joined: 22 Feb 2012
Posts: 88
GMAT 1: 740 Q49 V42 GMAT 2: 670 Q42 V40
GPA: 3.47
WE: Corporate Finance (Aerospace and Defense)

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
28 Mar 2012, 10:59
The 17/22 info can actually hurt you because if you built formulas for that portion it makes this way more complicated... Took me 4 mins of working on it that way to realize i was down the wrong path



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8187
Location: Pune, India

Re: Help with a ratio question.
[#permalink]
Show Tags
29 Mar 2012, 01:21
imhimanshu wrote: Hey Bunuel, While giving test, I have been able to solve it correctly using back solving. However, when I revisited this question, I was unable to solve it at the first go. Request you to help me out.. Let the multiplier be x for Class A . Therefore, number of boys: 3x and number of girls 4x Let the multiplier be y for Class B. Therefor, number of boys: 4y and number of girls : 5y It is given that  3x= 4y+1 (A) and 4x=5y+2 (B) Also As per question: 3x+4y/4x+5y = 17/22 (combined boys: combined girls) (C) Putting the value from A and B in Equation C giving me weird results  y is coming out to be 6/13 I have also gone through the replies posted above and I am not too sure that I would be able to ignore the superfluous statement in the real time exam... so hoping to see the solution utilizing the info. Thanks H Also, if you do use this equation, 3x+4y/4x+5y = 17/22, when you solve it, you get x = 3y/2. Put x = 3y/2 is one of the equations above, say 3x= 4y+1. 3*3y/2 = 4y + 1 y = 2 (you probably have a calculation error somewhere) So x = 3 Number of boys and girls in Class A is 3*3 and 4*3. Mind you, since you have already got two distinct equations (3x= 4y+1 and 4x=5y+2) with two variables, you can easily solve them to get the values of x and y. This question lets you make 3 equations but there are only 2 variables so you can use any 2 of those equations to get the value of the variables. Actually speaking, you should not be making any equations. You have the ratio 3:4 and 4:5 You know that the number of boys is class A is 1 more so try and multiply the ratios to figure out where you get a difference of 1. I should multiply 3:4 by a bigger number since the number of boys is more in class A. (3:4)*3 = 9:12 (4:5)*2 = 8:10 The numbers are very simple so you can arrive at the answer very quickly.
_________________
Karishma Veritas Prep GMAT Instructor
Save up to $1,000 on GMAT prep through 8/20! Learn more here >
GMAT selfstudy has never been more personalized or more fun. Try ORION Free!



Manager
Joined: 07 Sep 2011
Posts: 61
Location: United States
Concentration: Strategy, International Business
WE: General Management (Real Estate)

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
19 Apr 2012, 05:08
I will just plug in answers to arrive at decision.
I start with 10. If 10 girls in class A, the boys have to be some integer. With ratio of 3:4, it is not possible to have integer value.
I take 12 as girls, the boys will be 9. This is the answer but to ensure if I did correctly or not, I just add additional information to check ratio of class B. If I reduce 1 boy from 9, I have 8 boys in class B and 10 girls after reducing 2 girls from 12 girls. Thus the ratio of class B is coming out to be 8:10 or 4:5. This is given in the question stem.



Senior Manager
Joined: 23 Oct 2010
Posts: 362
Location: Azerbaijan
Concentration: Finance

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
09 May 2012, 10:15
(3x1)/(4x2)=4/5 find 4x sinxe x=3 , 4*3=12 girls in class A
_________________
Happy are those who dream dreams and are ready to pay the price to make them come true
I am still on all gmat forums. msg me if you want to ask me smth



Intern
Joined: 28 Feb 2012
Posts: 21
WE: Information Technology (Computer Software)

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
13 May 2012, 05:12
changhiskhan wrote: The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?
A. 8 B. 9 C. 10 D. 11 E. 12 Since it is given that the ratio of boys to girls in Class A is 3 to 4  so we can quickly eliminate the answer choices which are not multiples of 4. so ans can either be 8 0r 12. With 8 as answer  no of girls = 8 With 12 as answer  no of girls = 12 Now Class A has one more boy and two more girls than class B and also the ratio of boys to girls in Class B is 4 to 5. So we are looking for number of girls in B to be divisible by 5. With 8 as answer > Girls = 82 = 6. (Not possible) With 12 as answer > Girls = 122 = 5. So, answer = 12. ( E)



Intern
Joined: 12 Apr 2012
Posts: 18

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
17 May 2012, 04:01
I picked E after about 2:34, but I didn't finish working any algebra I started. As I was getting to about 2 minutes on this problem, I decided to focus just on the 3:4 ratio for class A. Since the number of Boys and Girls each have to be integers, I realized only A or E were possible solutions. At that point, given the time I had spent already, I settled for the 50/50 odds and picked E. If I had taken that approach immediately, it would have taken only a short amount of time to further test the solutions for fitting into the combined ratio. But I figure if this question came up at the end when I was running out of time to finish, that I could live with the 50/50 chance.
_________________
d_n_g_



Manager
Status: mba here i come!
Joined: 07 Aug 2011
Posts: 230

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
22 Aug 2012, 11:08
total # of girls = 22k (22, 44, 66 ..) if A has 2 more girls then # of girls in (a,b) = (12,10), (21,23) .. at this point, you know that it can only be 12 because 21 is not an option.
_________________
press +1 Kudos to appreciate posts Download Valuable Collection of Percentage Questions (PS/DS)



Retired Moderator
Status: 2000 posts! I don't know whether I should feel great or sad about it! LOL
Joined: 04 Oct 2009
Posts: 1358
Location: Peru
Schools: Harvard, Stanford, Wharton, MIT & HKS (Government)
WE 1: Economic research
WE 2: Banking
WE 3: Government: Foreign Trade and SMEs

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
24 Aug 2012, 10:44
+1 E The operations can be expressed with only two variables: boys in class B and girls in class B.
_________________
"Life’s battle doesn’t always go to stronger or faster men; but sooner or later the man who wins is the one who thinks he can."
My Integrated Reasoning Logbook / Diary: http://gmatclub.com/forum/myirlogbookdiary133264.html
GMAT Club Premium Membership  big benefits and savings



Director
Joined: 22 Mar 2011
Posts: 604
WE: Science (Education)

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
24 Aug 2012, 12:13
changhiskhan wrote: The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?
A. 8 B. 9 C. 10 D. 11 E. 12 The information the ratio of boys to girls in the combined class would be 17 to 22 is superfluous. Too much info just to try to confuse you. If one counts the unknowns, we have 4: number of boys in class A, girls in A, boys in B and girls in B. Without the info of the combined rate, we already have in fact four equations: 1) the ratio in class A 2) the ratio in class B 3) one more boy in class A in comparison with class B 4) two more girls in class A in comparison with class B So, we don't need a fifth equation. If we denote by B and G the number of boys and girls respectively in class A, we can write the following set of equations: \(B/G=3/4\) \((B1)/(G2)=4/5\) Two equations, two unknowns, solve and get G=12. Or, go with divisibility criteria, G must be a multiple of 4, so choose between A and E. For A, B=6, G=8 but B1=5, G2=6, so \(5/6\neq4/5\). For E, B=9, G=12 and B1=8, G2=10, so 8/10=4/5, OK. Also the additional condition holds, as (9+8)/(12+10)=17/22.
_________________
PhD in Applied Mathematics Love GMAT Quant questions and running.



Senior Manager
Joined: 13 Aug 2012
Posts: 441
Concentration: Marketing, Finance
GPA: 3.23

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
01 Dec 2012, 21:34
Too many given... Combination of class equations:\(3a + 4b = 17\) \(4a + 5b = 22\) Another given  Differences of class equations\(3a = 4b + 1\) \(4a = 5b + 2\) Combine \(3a + 4b = 17\) and \(3a = 4b + 1\)\(173a = 3a  1\) \(18 = 6a\) \(a = 3\) Answer: 4*3 = 12 (E)
_________________
Impossible is nothing to God.



SVP
Joined: 06 Sep 2013
Posts: 1851
Concentration: Finance

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
03 Jan 2014, 06:27
changhiskhan wrote: The ratio of boys to girls in Class A is 3 to 4. The ratio of boys to girls in Class B is 4 to 5. If the two classes were combined, the ratio of boys to girls in the combined class would be 17 to 22. If Class A has one more boy and two more girls than class B, how many girls are in Class A?
A. 8 B. 9 C. 10 D. 11 E. 12 Quick way to solve Class A B/G =3X/4X Class B B/G=4Y/5Y Also 3X = 4Y+1 (2) 4X = 5Y+2 We need to find 4x So we also get that 3x + 4y = 17 (1) 4x + 5y = 22 Now, those are quite a number of equations, but let's make the work easy ok? Since 3X= 4Y+1 Then I will add one to each side of (1) 3x + 4y+1=18 Now replace with (2) 6x = 18 x = 3 And finally, 4x will be 12 Answer is thus E Hope it helps! Gimme kuddos if you liked it Cheers! J



Intern
Joined: 07 Jan 2014
Posts: 1

The ratio of boys to girls in Class A is 3 to 4. The ratio of bo
[#permalink]
Show Tags
18 Jan 2014, 06:16
alimad wrote: So far i'm got :
Class A :
B/G = 3/4 = 4B = 3G = 4b3g = 0
Class B :
B/g = 4/5 = 5b4g = 0
Combined :
4b+4b1/3g+3g2 = 17/22
8b 1 /6g 2 = 17/22
8b/6g = 16/20
div by 2
4b/3g = 8/10
40b = 24g  I'm lost here.  well 4b+4b1=17 8b1=17 8b=16 b=2 3g+3g2=22 6g = 24 g= 4 substitute 'b' and 'g ' both in the equation 4b3g = 0 ull get B= 8 and G= 12



Manager
Joined: 11 Jan 2014
Posts: 93
Concentration: Finance, Statistics
GMAT Date: 03042014
GPA: 3.77
WE: Analyst (Retail Banking)

Re: The ratio of boys to girls in Class A is 3 to 4. The ratio
[#permalink]
Show Tags
18 Jan 2014, 13:33
Assuming I was short of time on the real test, is it safe to eliminate choices B,C and D on the spot? since 9,10,11 are not divisible by 4?




Re: The ratio of boys to girls in Class A is 3 to 4. The ratio &nbs
[#permalink]
18 Jan 2014, 13:33



Go to page
1 2 3
Next
[ 44 posts ]



