GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 18 Oct 2018, 21:50

### 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

# Solution A is 40% chlorine by volume, and Solution B is 60% chlorine

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 50000
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

10 Apr 2018, 00:05
00:00

Difficulty:

15% (low)

Question Stats:

91% (01:14) correct 9% (02:08) wrong based on 84 sessions

### HideShow timer Statistics

Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume. If a tank currently holds 40 gallons of Solution A, how many gallons of Solution B must be added so that the liquid in the tank is 50% chlorine?

A. 40 gallons
B. 50 gallons
C. 60 gallons
D. 80 gallons
E. 100 gallons

_________________
examPAL Representative
Joined: 07 Dec 2017
Posts: 715
Re: Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

10 Apr 2018, 00:15
1
Bunuel wrote:
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume. If a tank currently holds 40 gallons of Solution A, how many gallons of Solution B must be added so that the liquid in the tank is 50% chlorine?

A. 40 gallons
B. 50 gallons
C. 60 gallons
D. 80 gallons
E. 100 gallons

As mixture problems can often be solved based on properties of ratios, without explicit calculation, we'll look for such a solution.
This is a Logical approach.

We'd like the final concentration of chlorine in the tank to be 50%, exactly in the middle of the concentrations of solution A (40%) and solution B (60%).
That is, we want both of the solutions to affect the final concentration equally, meaning we want them to have equal volumes.
Since there were 40 gallons fo Solution A, we need to add 40 gallons of Solution B.

*Note: if the conentration weren't exactly in the middle, we would have needed to adjust accordingly. Say we want the final concentration to be 45%. This is 5% away from Solution A and 15% away from solution B for a ratio of 1:3. Then we need 3 times as much solution A as solution B (this ensure is has '3 times the effect' and our answer would be 40/3 gallons.
_________________

Watch free GMAT tutorials in Math, Verbal, IR, and AWA.

GMAT test takers: Watch now the GMAC interview with the people who write the GMAT test!
We discussed the chances of improving a GMAT score; how important the first questions on the test are; what to do if you don’t have enough time to complete a whole section; and more.

You can watch all the action from the interview here.

CEO
Joined: 08 Jul 2010
Posts: 2541
Location: India
GMAT: INSIGHT
WE: Education (Education)
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

10 Apr 2018, 02:18
Bunuel wrote:
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume. If a tank currently holds 40 gallons of Solution A, how many gallons of Solution B must be added so that the liquid in the tank is 50% chlorine?

A. 40 gallons
B. 50 gallons
C. 60 gallons
D. 80 gallons
E. 100 gallons

Please find the solution as attached.

Two methods mentioned.

Attachments

File comment: www.GMATinsight.com

GMATINSIGHT.jpg [ 1.15 MiB | Viewed 931 times ]

_________________

Prosper!!!
GMATinsight
Bhoopendra Singh and Dr.Sushma Jha
e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772
Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi
http://www.GMATinsight.com/testimonials.html

ACCESS FREE GMAT TESTS HERE:22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION

VP
Joined: 07 Dec 2014
Posts: 1104
Re: Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

10 Apr 2018, 11:21
Bunuel wrote:
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume. If a tank currently holds 40 gallons of Solution A, how many gallons of Solution B must be added so that the liquid in the tank is 50% chlorine?

A. 40 gallons
B. 50 gallons
C. 60 gallons
D. 80 gallons
E. 100 gallons

let x=gallons of solution B to be added
.4*40+.6*x=.5(40+x)
x=40 gallons
A
Senior SC Moderator
Joined: 22 May 2016
Posts: 2034
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

10 Apr 2018, 12:06
Bunuel wrote:
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume. If a tank currently holds 40 gallons of Solution A, how many gallons of Solution B must be added so that the liquid in the tank is 50% chlorine?

A. 40 gallons
B. 50 gallons
C. 60 gallons
D. 80 gallons
E. 100 gallons

10-second method:
The final solution's concentration (50%) is the average of A's (40%) and B's (60%) concentrations.

That can happen only if A and B have identical volumes. B's volume = A's = 40 gallons

Weighted average:

One version of weighted average formula:
(% A)(Vol A) + (% B)(Vol B) = (% of A+B)(Vol A+B)

A = 40% chlorine = .40
B = .60 chlorine
A's volume = 40
B's volume = x

$$.40(40) +.60(x) = .50(40+x)$$
$$16 + .60x = 20 + .50x$$
$$.10x = 4$$
$$x=\frac{4}{.1}=\frac{40}{1}=40$$
gallons

_________________

The only thing more dangerous than ignorance is arrogance.
-- Albert Einstein

Manager
Joined: 08 Sep 2016
Posts: 118
Re: Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

10 Apr 2018, 14:31
40A + 60B = 50A + 50B

10B = 10A

A/B = 1/1

For 1A added, there's 1B added since the ratio is 1 to 1. So if 40 gallons of A is in the tank, 40 gallons of B will need to be added to maintain the ratio.
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 3886
Location: United States (CA)
Re: Solution A is 40% chlorine by volume, and Solution B is 60% chlorine  [#permalink]

### Show Tags

11 Apr 2018, 16:19
Bunuel wrote:
Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume. If a tank currently holds 40 gallons of Solution A, how many gallons of Solution B must be added so that the liquid in the tank is 50% chlorine?

A. 40 gallons
B. 50 gallons
C. 60 gallons
D. 80 gallons
E. 100 gallons

Current there are 40 x 0.4 = 16 gallons of chlorine from solution A. We can let the amount of solution B = n and create the equation:

(16 + 0.6n)/(40 + n) = 1/2

2(16 + 0.6n) = 40 + n

32 + 1.2n = 40 + n

0.2n = 8

n = 40

_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Re: Solution A is 40% chlorine by volume, and Solution B is 60% chlorine &nbs [#permalink] 11 Apr 2018, 16:19
Display posts from previous: Sort by