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

 It is currently 18 Jun 2019, 06:20

### 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

# How many liters of pure alcohol must be added to a 90-liter solution

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 55668
How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

30 Jun 2017, 03:34
00:00

Difficulty:

25% (medium)

Question Stats:

78% (01:57) correct 22% (02:06) wrong based on 279 sessions

### HideShow timer Statistics

How many liters of pure alcohol must be added to a 90-liter solution that is 20 percent alcohol in order to produce a solution that is 25 percent alcohol?

(A) 4.5
(B) 5.0
(C) 5.5
(D) 6.0
(E) 6.5

_________________
Senior PS Moderator
Joined: 26 Feb 2016
Posts: 3373
Location: India
GPA: 3.12
Re: How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

30 Jun 2017, 04:10
1
We are given 90 liters of 20% alcohol,
for 18 liters of alcohol, we will have 72 liters of water.

If we want the solution to become 25% alcohol and add pure alcohol,
let the liters of pure alcohol to be added be x

$$\frac{18+x}{72} = \frac{1}{3}$$
54 + 3x = 72
3x = 18
Solution of pure alcohol to be added(x) = 6(Option D)
_________________
You've got what it takes, but it will take everything you've got
Manager
Joined: 03 Feb 2017
Posts: 74
Location: Australia
GMAT 1: 720 Q48 V40
Re: How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

30 Jun 2017, 06:33
2
1
The amount of alcohol in the 90% solution is 90*$$\frac{1}{5}$$=18 litres

We need to add some solution of pure alcohol to make the total alcohol 25% of the solution

We can use answer choices as it is easier
From D, if we add 6 litres alcohol to the solution, total alcohol will become 18+6=24 litres

Alcohol percent = $$\frac{24}{(90+6)}$$ = $$\frac{24}{96}$$ = $$\frac{1}{4}$$ = 25%

This fits the question, so D is the answer.
Senior SC Moderator
Joined: 22 May 2016
Posts: 2899
How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

30 Jun 2017, 06:38
Bunuel wrote:
How many liters of pure alcohol must be added to a 90-liter solution that is 20 percent alcohol in order to produce a solution that is 25 percent alcohol?

(A) 4.5
(B) 5.0
(C) 5.5
(D) 6.0
(E) 6.5

Let x = amount of alcohol to be added

(.20)90 + (1)x = .25 (90 + x)**

18 + x = 22.5 + .25x

.75x = 4.5

x = 6

**
The method:

90 liter solution is A

Amount of alcohol to be added is B

A + B = total volume of resultant solution

Concentration of pure alcohol is 100%, in decimal form = 1

(Concen. of A)(Vol of A) + (Concen of B)(Vol of B) = (Desired concentration of resultant solution)(Vol of resultant solution)
_________________
SC Butler has resumed!
Get two SC questions to practice, whose links you can find by date, here.

Tell me, what is it you plan to do with your one wild and precious life? -- Mary Oliver
Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 6563
Location: United States (CA)
Re: How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

04 Jul 2017, 07:48
1
Bunuel wrote:
How many liters of pure alcohol must be added to a 90-liter solution that is 20 percent alcohol in order to produce a solution that is 25 percent alcohol?

(A) 4.5
(B) 5.0
(C) 5.5
(D) 6.0
(E) 6.5

Our given solution has 90 x 0.2 = 18 liters of alcohol. We can let x = the number of liters of pure alcohol added and create the following equation:

1/4 = (18 + x)/(90 + x)

90 + x = 4(18 + x)

90 + x = 72 + 4x

18 = 3x

6 = x

_________________

# Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
122 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Intern
Joined: 03 Jan 2017
Posts: 19
Location: India
Concentration: Finance, Economics
Re: How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

10 Jul 2017, 16:37
Alcohol solution= 20% pure alcohol=100%

Required Alcohol%age= 25%

Therefore, alcohol solution must be=75% & pure alcohol must be= 5%
Which in ration is 15:1

We need the mixture in 15:1 form which contains 15 part of the alcohol solution and 1 part of pure alcohol. Since we are asked how many litres of pure alcohol needs to be added.

If 15 parts of alcohol solution is 90 litres, 1 part must be be 90/15 = 6

I'm not good at explanations.
Non-Human User
Joined: 09 Sep 2013
Posts: 11383
Re: How many liters of pure alcohol must be added to a 90-liter solution  [#permalink]

### Show Tags

27 Oct 2018, 05:56
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: How many liters of pure alcohol must be added to a 90-liter solution   [#permalink] 27 Oct 2018, 05:56
Display posts from previous: Sort by