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

 It is currently 21 Feb 2019, 20:44

### 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 February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar

February 21, 2019

February 21, 2019

10:00 PM PST

11:00 PM PST

Kick off your 2019 GMAT prep with a free 7-day boot camp that includes free online lessons, webinars, and a full GMAT course access. Limited for the first 99 registrants! Feb. 21st until the 27th.
• ### Free GMAT RC Webinar

February 23, 2019

February 23, 2019

07:00 AM PST

09:00 AM PST

Learn reading strategies that can help even non-voracious reader to master GMAT RC. Saturday, February 23rd at 7 AM PT

# How many ounces of pure acid must be added to 20 ounces of a solution

Author Message
TAGS:

### Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 53063
How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

05 Mar 2018, 20:30
00:00

Difficulty:

25% (medium)

Question Stats:

81% (01:59) correct 19% (02:28) wrong based on 134 sessions

### HideShow timer Statistics

How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

_________________
Math Expert
Joined: 02 Sep 2009
Posts: 53063
Re: How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

05 Mar 2018, 20:32
Bunuel wrote:
How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

18. Mixture Problems

For more check Ultimate GMAT Quantitative Megathread

Hope it helps.
_________________
Intern
Joined: 07 May 2017
Posts: 22
How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

05 Mar 2018, 22:24
2
Bunuel wrote:
How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

ANS: (B)

5% of 20 ounces=1
so now the question says what quantity of acid must be added to this 1 ounce of acid so that it becomes 24% of the new solution.
let the new quantity of acid to be added be x
total new quantity of acid=1+x
new quantity of solution = 20+x

Therefore 1+x= 24/100* (20+x) = solve and the answer is 5 ounces.

hope this is of some help!
_________________

EYES CANNOT SEE WHAT THE MIND DOES NOT KNOW !

Guiding Principle:A life which has done no good to the mankind is a life not lived !

Senior SC Moderator
Joined: 22 May 2016
Posts: 2491
How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

06 Mar 2018, 09:01
Bunuel wrote:
How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

To find the volume of one solution in a resultant mixture, weighted average works well. I use this formula:
$$(Concen_{A})(Vol_{A}) + (Concen_{B})(Vol_{B} = (Concen_{A+B})(Vol_{A+B})$$

Per the formula, in setting up the equation:
A = the solution that is 5% acid
B = the solution that is pure acid (100% = 1)
Let $$x$$= # of ounces of pure acid (B) to be added
Desired concentration of resultant mix: 24%=.24
A + B (volume) = 20 + x

$$.05(20) + 1(x) = .24 (20 + x)$$
$$1 + x = .24(20) +.24(x)$$
$$1 + x = 4.8 + .24x$$
$$.76x = 3.8$$
$$x =\frac{3.8}{.76}=\frac{380}{76}=5$$

We need 5 ounces of pure acid.

_________________

To live is the rarest thing in the world.
Most people just exist.

Oscar Wilde

Manager
Joined: 01 Feb 2017
Posts: 188
Re: How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

07 Mar 2018, 06:19
The Equation:
100x + 20*5 = 24(x+20)

Simplifying, we get
76x = (24-5)*20 = 19*20

Therefore, x=5.

Ans B

Posted from my mobile device
Target Test Prep Representative
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2827
Re: How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

08 Mar 2018, 10:42
Bunuel wrote:
How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

We can let n = the number of ounces of pure (100%) acid added to the solution.

(0.05)(20) + n = 0.24(20 + n)

1 + n = 4.8 + 0.24n

0.76n = 3.8

n = 5

_________________

Jeffery Miller

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

Intern
Joined: 28 Feb 2018
Posts: 7
Re: How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

11 Mar 2018, 01:46
Bunuel wrote:
How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

Keep it Simple!

=> Non Acid before = Non Acid After
=> 95% of 20 = 76% of (20+x)
=> 19 = 76/100*(20+x)
=> 25 = 20+x
=> x = 5
VP
Joined: 07 Dec 2014
Posts: 1153
Re: How many ounces of pure acid must be added to 20 ounces of a solution  [#permalink]

### Show Tags

11 Mar 2018, 12:28
Bunuel wrote:
How many ounces of pure acid must be added to 20 ounces of a solution that is 5% acid to strengthen it to a solution that is 24% acid?

(A) 5/2

(B) 5

(C) 6

(D) 15/2

(E) 10

let a=ounces of acid to be added
.05*20+a=.24*(20+a)
a=5 ounces
B
Re: How many ounces of pure acid must be added to 20 ounces of a solution   [#permalink] 11 Mar 2018, 12:28
Display posts from previous: Sort by