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

Redeem

The ratio of water and ammonia

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 366
Joined: Fri Jun 05, 2015 3:35 am
Thanked: 3 times
Followed by:2 members

The ratio of water and ammonia

by NandishSS » Tue Oct 24, 2017 7:11 am
The ratio of water and ammonia in solution A is 1 : 4; the ratio of the same two substances in solution B is 3 : 1. If solutions A and B are mixed, what will be the ratio of water and ammonia in the resultant solution?

(1) Solutions A and B are mixed in ratio 2 : 3.
(2) 20 liters of solution A is used

OA: A

Hi Experts,

Can you pls explain this problem?

Thanks
Nandish
Top
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 2663
Joined: Wed Jan 14, 2015 8:25 am
Location: Boston, MA
Thanked: 1153 times
Followed by:128 members
GMAT Score:770

by DavidG@VeritasPrep » Tue Oct 24, 2017 7:31 am
NandishSS wrote:The ratio of water and ammonia in solution A is 1 : 4; the ratio of the same two substances in solution B is 3 : 1. If solutions A and B are mixed, what will be the ratio of water and ammonia in the resultant solution?

(1) Solutions A and B are mixed in ratio 2 : 3.
(2) 20 liters of solution A is used

OA: A

Hi Experts,

Can you pls explain this problem?

Thanks
Nandish
Solution A
water: 1x
ammonia: 4x
total: 5x.

So A is 1/x/5x = 20% water

Solution B
water: 3y
ammonia: y
total: 4y.

So B is 3y/4y = 75% water

(Notice that if we had equal amounts of A and B, the percentage of water in our overall solution would be exactly halfway between 20 and 75.)

Statement 1: If the ratio of A to B is 2:3, we know there's a little more B than A in the solution, so we're pulled a little more toward the 75 than we are toward the 20. If we were to plot the water percentages on a number line, the distances from A and B to the overall average, can be represented as 3t and 2t respectively.

20----------------- Average--------75
Dist:------ 3t-----Average--2t----

Total distance between 20 and 75 = 3t + 2t = 5t.
5t = 55
t = 11

20 + 3t = 20 + 3*11 = 53. So the combined solution is 53% water and 47% ammonia. Sufficient. (Notice that we don't have to solve here. We have to see that it's possible to solve.)


Statement 2: tells us nothing about the quantity of Solution B. Not Sufficient.

The Answer is A
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Tue Oct 24, 2017 8:22 am
NandishSS wrote:The ratio of water and ammonia in solution A is 1 : 4; the ratio of the same two substances in solution B is 3 : 1. If solutions A and B are mixed, what will be the ratio of water and ammonia in the resultant solution?

(1) Solutions A and B are mixed in ratio 2 : 3.
(2) 20 liters of solution A is used
Question stem, rephrased:
What fraction of the resultant solution is water?

Statement 1:
Case 1: A=20 liters and B=30 liters, for a total of 50 liters
Since A is 1/5 water, the amount of water in 20 liters of A = (1/5)(20) = 4.
Since B is 3/4 water, the amount of water in 30 liters of B = (3/4)(30) = 22.5.
Thus, (total water)/(total volume) = (4 + 22.5)/50 = 26.5/50 = 53/100.

Case 2: A=40 liters and B=60 liters, for a total of 100 liters
Since A is 1/5 water, the amount of water in 40 liters of A = (1/5)(40) = 8.
Since B is 3/4 water, the amount of water in 60 liters of B = (3/4)(60) = 45.
Thus, (total water)/(total volume) = (8 + 45)/100 = 53/100.

Since (total water)/(total volume) is THE SAME VALUE in each case -- 53/100 --
Statement 1 is SUFFICIENT.

Statement 2:
No information about the amount of B in the resultant solution.
INSUFFICIENT.

The correct answer is A.
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
Post new topic Post Reply
• Page 1 of 1