BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Ratios and Mixtures

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 19
Joined: Wed May 26, 2010 2:26 am
by Shridharvk » Tue Aug 10, 2010 6:42 am
The ratio, by volume, of acid to base to water in a certain solution is 4:15:20. The solution is altered so that the
ratio of acid to base is 3:5 and the ratio of acid to water remains same. If the solution initially contained 30mm
of base, what is the minimum amount of water that could be added in the second phase?

A) 18 B) 36 C) 50 D) 60 E) 90

Can someone help me in solving this question please?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Tue Aug 10, 2010 7:11 am
Shridharvk wrote:The ratio, by volume, of acid to base to water in a certain solution is 4:15:20. The solution is altered so that the
ratio of acid to base is 3:5 and the ratio of acid to water remains same. If the solution initially contained 30mm
of base, what is the minimum amount of water that could be added in the second phase?

A) 18 B) 36 C) 50 D) 60 E) 90

Can someone help me in solving this question please?
Original A:B:W = 4:15:20.
B = 30, so actual values of A, B and W are all doubled:
A = 8
B = 30
W = 40

New ratio of A:B = 3:5
Unchanged ratio of A:W = 4:20 = 1:5 = 3:15 (Since A is common to each ratio, we want A to be represented by the same number in each ratio so that the ratios can be combined.)
So combining the ratios, we get a new ratio of A:B:W = 3:5:15.

We want to minimize the amount of water added, so we should keep B=30.
A:B:W = 3:5:15 = 18:30:90. (Every value in 3:5:15 is multiplied by 6 so that B=30.)
So new A=18.
B=30.
new W=90.
So new W - old W = 90-40=50.

The correct answer is C.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Junior | Next Rank: 30 Posts
Posts: 18
Joined: Thu Aug 05, 2010 3:44 am

by rahul goyal » Tue Aug 10, 2010 9:38 pm
GMATGuruNY wrote:
Shridharvk wrote:The ratio, by volume, of acid to base to water in a certain solution is 4:15:20. The solution is altered so that the
ratio of acid to base is 3:5 and the ratio of acid to water remains same. If the solution initially contained 30mm
of base, what is the minimum amount of water that could be added in the second phase?

A) 18 B) 36 C) 50 D) 60 E) 90

Can someone help me in solving this question please?
Original A:B:W = 4:15:20.
B = 30, so actual values of A, B and W are all doubled:
A = 8
B = 30
W = 40

New ratio of A:B = 3:5
Unchanged ratio of A:W = 4:20 = 1:5 = 3:15 (Since A is common to each ratio, we want A to be represented by the same number in each ratio so that the ratios can be combined.)
So combining the ratios, we get a new ratio of A:B:W = 3:5:15.

We want to minimize the amount of water added, so we should keep B=30.
A:B:W = 3:5:15 = 18:30:90. (Every value in 3:5:15 is multiplied by 6 so that B=30.)
So new A=18.
B=30.
new W=90.
So new W - old W = 90-40=50.

The correct answer is C.
Thank you verymuch GMATGuruNY .But i want little bit clear here,
why we should keep B=30.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Senior | Next Rank: 100 Posts
Posts: 37
Joined: Thu Aug 05, 2010 3:15 am

by aarati » Tue Aug 10, 2010 10:28 pm
GMATGuruNY wrote: Original A:B:W = 4:15:20.
B = 30, so actual values of A, B and W are all doubled:
A = 8
B = 30
W = 40

New ratio of A:B = 3:5
Unchanged ratio of A:W = 4:20 = 1:5 = 3:15 (Since A is common to each ratio, we want A to be represented by the same number in each ratio so that the ratios can be combined.)
So combining the ratios, we get a new ratio of A:B:W = 3:5:15.

We want to minimize the amount of water added, so we should keep B=30.
A:B:W = 3:5:15 = 18:30:90. (Every value in 3:5:15 is multiplied by 6 so that B=30.)
So new A=18.
B=30.
new W=90.
So new W - old W = 90-40=50.

The correct answer is C.
thank you.. but i am totally confused..can u explain me little bit clear .....
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 2326
Joined: Mon Jul 28, 2008 3:54 amFollowed by: 2 members
Thanked: 173 times
GMAT Score:710

by gmatmachoman » Wed Aug 11, 2010 12:40 am
rahul goyal wrote: , so we should keep B=30.

The correct answer is C.
Thank you verymuch GMATGuruNY .But i want little bit clear here,
why we should keep B=30.[/quote]


It is stated in the stem that BASE (B) is " If the solution initially contained 30mm
of base" . So B is 30
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Wed Aug 11, 2010 2:35 am
rahul goyal wrote:
GMATGuruNY wrote:
Shridharvk wrote:The ratio, by volume, of acid to base to water in a certain solution is 4:15:20. The solution is altered so that the
ratio of acid to base is 3:5 and the ratio of acid to water remains same. If the solution initially contained 30mm
of base, what is the minimum amount of water that could be added in the second phase?

A) 18 B) 36 C) 50 D) 60 E) 90

Can someone help me in solving this question please?
Original A:B:W = 4:15:20.
B = 30, so actual values of A, B and W are all doubled:
A = 8
B = 30
W = 40

New ratio of A:B = 3:5
Unchanged ratio of A:W = 4:20 = 1:5 = 3:15 (Since A is common to each ratio, we want A to be represented by the same number in each ratio so that the ratios can be combined.)
So combining the ratios, we get a new ratio of A:B:W = 3:5:15.

We want to minimize the amount of water added, so we should keep B=30.
A:B:W = 3:5:15 = 18:30:90. (Every value in 3:5:15 is multiplied by 6 so that B=30.)
So new A=18.
B=30.
new W=90.
So new W - old W = 90-40=50.

The correct answer is C.
Thank you verymuch GMATGuruNY .But i want little bit clear here,
why we should keep B=30.
In the original mixture, A=8, B=30, W=40.
The new ratio is A:B:W = 3:5:15.
We want to increase W by the smallest amount possible.
Since B is proportional to W, the smallest possible value of B will give us the smallest possible value of W.
We can't remove any base, so we can't decrease B. B=30 is the smallest possible value of B.
In the new ratio if B=30, then W=90. (B/W = 5/15 = 30/90).
So in the new ratio W=90 is the smallest possible value of W.

New W - old W = 90 - 40 = 50.

Does this help?
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 217
Joined: Sun Jan 10, 2010 1:39 pmFollowed by: 1 member
Thanked: 7 times

by zaarathelab » Mon Oct 17, 2011 6:24 am
Mitch, I don't understand why we can't decrease the value of B beyond 30. When it says that the new ratio is 3:5:15, the new ratio could have been formed after decreasing their individual quantities.

The multiplying factor for the new ratio could be 1. In which case water could be 15mm. which is lower than 40mm!

I might be missing something in this question!
Success = Max(Hardwork) + Min(Luck)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 105
Joined: Fri Nov 05, 2010 8:29 pm
Thanked: 4 times

by nandy1984 » Mon Oct 17, 2011 10:00 am
GMATGuruNY wrote:
rahul goyal wrote:
GMATGuruNY wrote:
Shridharvk wrote:The ratio, by volume, of acid to base to water in a certain solution is 4:15:20. The solution is altered so that the
ratio of acid to base is 3:5 and the ratio of acid to water remains same. If the solution initially contained 30mm
of base, what is the minimum amount of water that could be added in the second phase?

A) 18 B) 36 C) 50 D) 60 E) 90

Can someone help me in solving this question please?
Original A:B:W = 4:15:20.
B = 30, so actual values of A, B and W are all doubled:
A = 8
B = 30
W = 40

New ratio of A:B = 3:5
Unchanged ratio of A:W = 4:20 = 1:5 = 3:15 (Since A is common to each ratio, we want A to be represented by the same number in each ratio so that the ratios can be combined.)
So combining the ratios, we get a new ratio of A:B:W = 3:5:15.

We want to minimize the amount of water added, so we should keep B=30.
A:B:W = 3:5:15 = 18:30:90. (Every value in 3:5:15 is multiplied by 6 so that B=30.)
So new A=18.
B=30.
new W=90.
So new W - old W = 90-40=50.

The correct answer is C.
Thank you verymuch GMATGuruNY .But i want little bit clear here,
why we should keep B=30.
In the original mixture, A=8, B=30, W=40.
The new ratio is A:B:W = 3:5:15.
We want to increase W by the smallest amount possible.
Since B is proportional to W, the smallest possible value of B will give us the smallest possible value of W.
We can't remove any base, so we can't decrease B. B=30 is the smallest possible value of B.
In the new ratio if B=30, then W=90. (B/W = 5/15 = 30/90).
So in the new ratio W=90 is the smallest possible value of W.

New W - old W = 90 - 40 = 50.

Does this help?
GMATguruNY, couldnot understand why we need to take b =30 inorder to minimize water...Please explain it by using different values for A,B and W. or by explaining what happens to value of W if B is not chosen 30...Thanks....
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Mon Oct 17, 2011 11:14 am
zaarathelab wrote:Mitch, I don't understand why we can't decrease the value of B beyond 30. When it says that the new ratio is 3:5:15, the new ratio could have been formed after decreasing their individual quantities.

The multiplying factor for the new ratio could be 1. In which case water could be 15mm. which is lower than 40mm!

I might be missing something in this question!
My solution above reflects the intention of the question: that the amount of base cannot be reduced and must be at least 30mm.
If the amount of base can be reduced, then it is not necessary to add ANY water, and the question has no correct answer.

The writer of the question apparently assumed that it would not be possible to EXTRACT base from the solution and that the only way to yield the desired ratio would be to ADD ingredients.

To any chemists out there: is it possible to extract only base from a solution of acid, base and water?
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 217
Joined: Sun Jan 10, 2010 1:39 pmFollowed by: 1 member
Thanked: 7 times

by zaarathelab » Tue Oct 18, 2011 1:16 am
GMATGuruNY wrote:
zaarathelab wrote:Mitch, I don't understand why we can't decrease the value of B beyond 30. When it says that the new ratio is 3:5:15, the new ratio could have been formed after decreasing their individual quantities.

The multiplying factor for the new ratio could be 1. In which case water could be 15mm. which is lower than 40mm!

I might be missing something in this question!
My solution above reflects the intention of the question: that the amount of base cannot be reduced and must be at least 30mm.
If the amount of base can be reduced, then it is not necessary to add ANY water, and the question has no correct answer.

The writer of the question apparently assumed that it would not be possible to EXTRACT base from the solution and that the only way to yield the desired ratio would be to ADD ingredients.

To any chemists out there: is it possible to extract only base from a solution of acid, base and water?
Mitch, your approach is right. These questions can be tricky at times. BTW this one is from GMAT paper tests.
Success = Max(Hardwork) + Min(Luck)
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 258
Joined: Fri Jun 22, 2012 4:39 amFollowed by: 3 members
Location: Bengaluru, India
Thanked: 6 times
GMAT Score:640

by sachindia » Wed Oct 17, 2012 7:29 pm
To any chemists out there: is it possible to extract only base from a solution of acid, base and water?
:) :)

nice sense of humor!
Regards,
Sach
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1