It is currently 25 Jun 2017, 03:35

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

The volume of water in a certain tank is x percent greater

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

Hide Tags

Director
Joined: 29 Nov 2012
Posts: 878
The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jan 2013, 01:49
1
KUDOS
19
This post was
BOOKMARKED
00:00

Difficulty:

45% (medium)

Question Stats:

72% (03:19) correct 28% (02:17) wrong based on 414 sessions

HideShow timer Statistics

The volume of water in a certain tank is x percent greater than it was one week ago. If r percent of the current volume of water in the tank is removed, the resulting volume will be 90 percent of the volume it was one week ago. What is the value of r in terms of x?

A. $$x+10$$

B. $$10x+1$$

C. $$100(x+10)$$

D. $$100( \frac{x+10}{x+100})$$

E. $$100 ( \frac{10x+1}{10x+10})$$
[Reveal] Spoiler: OA

_________________

Click +1 Kudos if my post helped...

Amazing Free video explanation for all Quant questions from OG 13 and much more http://www.gmatquantum.com/og13th/

GMAT Prep software What if scenarios http://gmatclub.com/forum/gmat-prep-software-analysis-and-what-if-scenarios-146146.html

Last edited by fozzzy on 20 Jul 2013, 22:41, edited 2 times in total.
VP
Status: Top MBA Admissions Consultant
Joined: 24 Jul 2011
Posts: 1250
GMAT 1: 780 Q51 V48
GRE 1: 1540 Q800 V740
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jan 2013, 03:42
1
KUDOS
1
This post was
BOOKMARKED
Volume now is x% greater than volume one week ago
=> Vnow = Vweekago (1+x/100)

If r percent of the current volume is removed, the resulting volume will be 90 percent of the volume a week ago
=> Vnow (1-r/100) = 0.9*Vweekago

Using the first equation, Vnow/Vweekago = (1+x/100)
Putting this in the second equation,
(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000
=> r = 100 - [9000/(100+x)]
=> r = 100* (10+x)/(100+x)

Option D
_________________

GyanOne | Top MBA Rankings and MBA Admissions Blog

Top MBA Admissions Consulting | Top MiM Admissions Consulting

Premium MBA Essay Review|Best MBA Interview Preparation|Exclusive GMAT coaching

Get a FREE Detailed MBA Profile Evaluation | Call us now +91 98998 31738

Current Student
Joined: 27 Jun 2012
Posts: 411
Concentration: Strategy, Finance
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jan 2013, 03:54
20
KUDOS
7
This post was
BOOKMARKED
Best approach for solving this specific problem would be "Pick numbers". You can also solve it in Algebraic way, but it could be time consuming and tedious.

Given that, the water was increased by x percent -> then reduced by r percent -> to 90 percent of what it was one week ago.
Consider, the 100 units of water was increased by 20% to 120 units -> then reduced by 25% of 120 (i.e. by 30 units) -> to 90 units.
i.e. Pick numbers as x = 20% and r = 25%

Substitute x=20 and identify the answer that gives r=25
A) x+10 --20+1=30
b) 10x+1 --200+1=201
c) 100(x+10) --100(20+10)=3000
d) 100( x+10/x+100) --100(20+10/20+100) = 100(30/120)=25
e) 100 ( 10x+1/10x+10) -- 100(200+1/200+10)= 100(201/210)

Hence choice(D) is the answer.
_________________

Thanks,
Prashant Ponde

Tough 700+ Level RCs: Passage1 | Passage2 | Passage3 | Passage4 | Passage5 | Passage6 | Passage7
VOTE GMAT Practice Tests: Vote Here
PowerScore CR Bible - Official Guide 13 Questions Set Mapped: Click here

Moderator
Joined: 01 Sep 2010
Posts: 3211
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jan 2013, 10:24
PraPon wrote:
Best approach for solving this specific problem would be "Pick numbers". You can also solve it in Algebraic way, but it could be time consuming and tedious.

Given that, the water was increased by x percent -> then reduced by r percent -> to 90 percent of what it was one week ago.
Consider, the 100 units of water was increased by 20% to 120 units -> then reduced by 25% of 120 (i.e. by 30 units) -> to 90 units.
i.e. Pick numbers as x = 20% and r = 25%

Substitute x=20 and identify the answer that gives r=25
A) x+10 --20+1=30
b) 10x+1 --200+1=201
c) 100(x+10) --100(20+10)=3000
d) 100( x+10/x+100) --100(20+10/20+100) = 100(30/120)=25
e) 100 ( 10x+1/10x+10) -- 100(200+1/200+10)= 100(201/210)

Hence choice(D) is the answer.

I think that in this scenario under pressure someone could not visualize 25% to obtain 90 and to go in the wrong way.

better an hybrid approach and in this case algebraic translation maybe is a bit safer
_________________
Current Student
Joined: 27 Jun 2012
Posts: 411
Concentration: Strategy, Finance
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jan 2013, 16:09
2
KUDOS
2
This post was
BOOKMARKED
Yes I agree, not all problems can be solved using pick numbers strategy or not always will be able to come up with ideal pick numbers under pressure. At times for complex problems, you need pen down that lengthy/heavy algebraic computations. However, giving 5 seconds to think about execution method (pick numbers, backsolving or algebraic) after reading the problem, can help saving over 40-50 seconds of 'extra' time taken by algebraic method.

In this specific problem, I tried to visualize how can I increase 100 to certain number and decrease to obtain 90?? First comes 110, but reducing it by 20 doesnt give integer percentage on 110. Next we have 120 that includes 20% increase and then 25% decrease gives 90..bingo! It took 5-7 seconds to think & 15-20 seconds to back-solve, but saved 40-50 seconds of algebraic calculations!

Picking number requires strategy of identifying optimum numbers using LCM, LCD, prime factors, multiples of 10/100s.

How do we get used to this method? Practice!!

When solving OG or practice problems, always see if you can solve it using multiple ways. Try same problem with Algebra, back-solving, pick numbers, hybrid approach (whichever methods are applicable) and even try guessing it. You may also automatically build that intuition over the time.
_________________

Thanks,
Prashant Ponde

Tough 700+ Level RCs: Passage1 | Passage2 | Passage3 | Passage4 | Passage5 | Passage6 | Passage7
VOTE GMAT Practice Tests: Vote Here
PowerScore CR Bible - Official Guide 13 Questions Set Mapped: Click here

Moderator
Joined: 01 Sep 2010
Posts: 3211
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jan 2013, 16:44
1
KUDOS
Another consideration. be flexible

here we have something go up for a certain % and the go down for a certain % to have some result, here is 90. Ok 90 is our target value or our landmark

but what about if we think in a more abstract way ?? even if I increase my % of 20 or 30 and then decrease the same by any % to obtain a value of less than 100........the process is the same.

The gmat questions are so consistent and coherent (two word to say the same thing, indeed) that if you use several approachs they conduct you to the same answer, MUST conduct you to the same place. For this reason you can attack a problem with different stategies

Infact, even if you have 85 and not 90 as target value the answer is still D. Of course , this kind of resilience is acquired after you repeat over and over again the concepts behind
_________________
Intern
Joined: 19 Dec 2012
Posts: 1
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

26 Jan 2013, 07:43
PraPon wrote:
Best approach for solving this specific problem would be "Pick numbers". You can also solve it in Algebraic way, but it could be time consuming and tedious.

Given that, the water was increased by x percent -> then reduced by r percent -> to 90 percent of what it was one week ago.
Consider, the 100 units of water was increased by 20% to 120 units -> then reduced by 25% of 120 (i.e. by 30 units) -> to 90 units.
i.e. Pick numbers as x = 20% and r = 25%

Substitute x=20 and identify the answer that gives r=25
A) x+10 --20+1=30
b) 10x+1 --200+1=201
c) 100(x+10) --100(20+10)=3000
d) 100( x+10/x+100) --100(20+10/20+100) = 100(30/120)=25
e) 100 ( 10x+1/10x+10) -- 100(200+1/200+10)= 100(201/210)

Hence choice(D) is the answer.

Thanks so much for this way. My owm method costs me 5 minutes to solve this question.
The most difficult point is to estimate x and r as interger (First time I tried picking randomly and reached r=2/11% which made me unable to put into the formula).
I try starting with 100 as the amount of water last week --> the amount of water this week after removing r percent is 90% of 100 = 90.
I figure out r and x by finding a common multiple of 9 and 10 and larger than 100 (e.g. 180) --> figure out 180 for the first week (x=80%) and r=50%.
Manager
Joined: 28 Aug 2012
Posts: 52
Concentration: Operations, Marketing
GMAT 1: 510 Q36 V25
GPA: 4
WE: Information Technology (Other)
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

28 Jan 2013, 14:39
Hey!
I chose volume = 100 , x=5% , r=10%
Help plz?
Thanks
Aj
Senior Manager
Joined: 23 Oct 2010
Posts: 383
Location: Azerbaijan
Concentration: Finance
Schools: HEC '15 (A)
GMAT 1: 690 Q47 V38
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

29 Jan 2013, 06:22
(1+x/100)*V-(1+x/100)v*r/100=9/10*V (V is an initial volume)

solve this and u will get the answer D
_________________

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: 20 Jul 2013
Posts: 2
GMAT 1: 760 Q49 V44
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jul 2013, 08:00
1
KUDOS
Not quite sure I fully understand the algebra here

For x percent greater than original amount (v), wouldn't it be v*(100+x/100)? Why are the equations posted v*(1+x/100)?

to solve this problem I set up my equation like so:

v*(100+x/100)(100-r/100) = (90/100)*v

Any help is greatly appreciated!!!
Director
Joined: 29 Nov 2012
Posts: 878
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jul 2013, 08:41
1
KUDOS
Its actually the same if you cross multiply you arrive at the same equation. Since the question talks about percent increase its easier to write that way

For example if the question was
1000 is increased by X % and then by y % it would be $$1000( 1 + \frac{x}{100})(1+\frac{y}{100})$$
_________________

Click +1 Kudos if my post helped...

Amazing Free video explanation for all Quant questions from OG 13 and much more http://www.gmatquantum.com/og13th/

GMAT Prep software What if scenarios http://gmatclub.com/forum/gmat-prep-software-analysis-and-what-if-scenarios-146146.html

Intern
Joined: 20 Jul 2013
Posts: 2
GMAT 1: 760 Q49 V44
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

20 Jul 2013, 09:22
I carried it through and it worked. I was making a multiplication error. Thanks, I'm going to try the (1 + x/100) method from now on.
Manager
Joined: 01 Jan 2013
Posts: 63
Location: India
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

17 Oct 2013, 03:34
carcass wrote:
PraPon wrote:
Best approach for solving this specific problem would be "Pick numbers". You can also solve it in Algebraic way, but it could be time consuming and tedious.

Given that, the water was increased by x percent -> then reduced by r percent -> to 90 percent of what it was one week ago.
Consider, the 100 units of water was increased by 20% to 120 units -> then reduced by 25% of 120 (i.e. by 30 units) -> to 90 units.
i.e. Pick numbers as x = 20% and r = 25%

Substitute x=20 and identify the answer that gives r=25
A) x+10 --20+1=30
b) 10x+1 --200+1=201
c) 100(x+10) --100(20+10)=3000
d) 100( x+10/x+100) --100(20+10/20+100) = 100(30/120)=25
e) 100 ( 10x+1/10x+10) -- 100(200+1/200+10)= 100(201/210)

Hence choice(D) is the answer.

I think that in this scenario under pressure someone could not visualize 25% to obtain 90 and to go in the wrong way.

better an hybrid approach and in this case algebraic translation maybe is a bit safer

. 120 to 90 is just a percentage decrease from 120 to 90 120-90/120 = 1/4 =25% decrease
Current Student
Joined: 06 Sep 2013
Posts: 1997
Concentration: Finance
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

29 Dec 2013, 10:51
GyanOne wrote:
Volume now is x% greater than volume one week ago
=> Vnow = Vweekago (1+x/100)

If r percent of the current volume is removed, the resulting volume will be 90 percent of the volume a week ago
=> Vnow (1-r/100) = 0.9*Vweekago

Using the first equation, Vnow/Vweekago = (1+x/100)
Putting this in the second equation,
(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000
=> r = 100 - [9000/(100+x)]
=> r = 100* (10+x)/(100+x)

Option D

How did you get from here to here?
=> r = 100 - [9000/(100+x)]
=> r = 100* (10+x)/(100+x)

Thanks

Cheers!
J
Math Expert
Joined: 02 Sep 2009
Posts: 39666
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

29 Dec 2013, 11:11
jlgdr wrote:
GyanOne wrote:
Volume now is x% greater than volume one week ago
=> Vnow = Vweekago (1+x/100)

If r percent of the current volume is removed, the resulting volume will be 90 percent of the volume a week ago
=> Vnow (1-r/100) = 0.9*Vweekago

Using the first equation, Vnow/Vweekago = (1+x/100)
Putting this in the second equation,
(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000
=> r = 100 - [9000/(100+x)]
=> r = 100* (10+x)/(100+x)

Option D

How did you get from here to here?
=> r = 100 - [9000/(100+x)]
=> r = 100* (10+x)/(100+x)

Thanks

Cheers!
J

$$r = 100 - \frac{9000}{100+x}$$;

$$r = \frac{100*(100+x) - 9000}{100+x}$$;

$$r = \frac{100*(10+x)}{100+x}$$.

Hope it's clear.
_________________
Intern
Joined: 13 Feb 2013
Posts: 12
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

04 Jul 2014, 12:10
(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000

I am seriously having a brain fart, how do you get the 9000. I multiplied everything by 100.
Math Expert
Joined: 02 Sep 2009
Posts: 39666
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

05 Jul 2014, 07:07
syu322 wrote:
(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000

I am seriously having a brain fart, how do you get the 9000. I multiplied everything by 100.

You should have multiplied by 100*100:

$$(1-\frac{r}{100}) (1+\frac{x}{100}) =0.9$$;

$$(\frac{100-r}{100}) (\frac{100+x}{100}) = 0.9$$;

$$(100 - r) (100 + x) = 0.9*100*100=9000$$.

Hope it's clear.
_________________
Current Student
Joined: 27 Sep 2012
Posts: 7
Location: United States
GMAT 1: 750 Q49 V44
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

16 Jul 2014, 16:34
Bunuel wrote:
syu322 wrote:
(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000

I am seriously having a brain fart, how do you get the 9000. I multiplied everything by 100.

You should have multiplied by 100*100:

$$(1-\frac{r}{100}) (1+\frac{x}{100}) =0.9$$;

$$(\frac{100-r}{100}) (\frac{100+x}{100}) = 0.9$$;

$$(100 - r) (100 + x) = 0.9*100*100=9000$$.

Hope it's clear.

As per question if r percent is removed then remaining is 90 % of original. Can we infer that removed water is 10% of the original. Hence i used this equation

(r/100)*[1+x/100] V= 0.1 V..Which gave me wrong answer....Help please
Math Expert
Joined: 02 Sep 2009
Posts: 39666
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

16 Jul 2014, 17:00
sachin6016 wrote:
Bunuel wrote:
syu322 wrote:
The volume of water in a certain tank is x percent greater than it was one week ago. If r percent of the current volume of water in the tank is removed, the resulting volume will be 90 percent of the volume it was one week ago. what is the value of r in terms of x?

A. $$x+10$$

B. $$10x+1$$

C. $$100(x+10)$$

D. $$100( \frac{x+10}{x+100})$$

E. $$100 ( \frac{10x+1}{10x+10})$$

(1-r/100) (1+x/100) = 0.9
=> (100 - r) (100 + x) = 9000

I am seriously having a brain fart, how do you get the 9000. I multiplied everything by 100.

You should have multiplied by 100*100:

$$(1-\frac{r}{100}) (1+\frac{x}{100}) =0.9$$;

$$(\frac{100-r}{100}) (\frac{100+x}{100}) = 0.9$$;

$$(100 - r) (100 + x) = 0.9*100*100=9000$$.

Hope it's clear.

As per question if r percent is removed then remaining is 90 % of original. Can we infer that removed water is 10% of the original. Hence i used this equation

(r/100)*[1+x/100] V= 0.1 V..Which gave me wrong answer....Help please

No, that's not correct.

The volume of water one week ago = 100 (that's what I believe you call original);

The volume of water now is x=20% greater = 120.

The volume of water after removal of r% of 120 = 90.

So, as you can see r% is not 10% of 100, it's r% of 120, which result in final volume of 90.

Does this make sense?
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 15964
Re: The volume of water in a certain tank is x percent greater [#permalink]

Show Tags

21 Aug 2015, 23:52
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.
_________________
Re: The volume of water in a certain tank is x percent greater   [#permalink] 21 Aug 2015, 23:52

Go to page    1   2    Next  [ 24 posts ]

Similar topics Replies Last post
Similar
Topics:
2 The ratio, by volume, of acid to base to water in a certain solution 3 25 Jun 2017, 00:58
5 A certain pipe carries water between two tanks such that the height of 5 07 May 2017, 18:36
10 Solution Y is 40 percent sugar by volume, and solution X is 20 percent 7 06 Jan 2017, 08:18
68 Tanks X and Y contain 500 and 200 gallons of water respectiv 30 14 Oct 2016, 14:00
2 The concentration of a certain chemical in a full water tank 4 11 Apr 2014, 04:03
Display posts from previous: Sort by

The volume of water in a certain tank is x percent greater

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.