A chemist is mixing a solution of acetone and water. She currently has

Question

A chemist is mixing a solution of acetone and water. She currently has 30 ounces mixed, 10 of which are acetone. How many ounces of acetone should she add to her current mixture to attain a 50/50 mixture of acetone and water if no additional water is added?

(A) 2.5
(B) 5
(C) 10
(D) 15
(E) 20

(A) 2.5 
(B) 5 
(C) 10 
(D) 15 
(E) 20

alldaytestprep · Answer

Old acetone = 10
Acetone added = x 
Old total = 30

---> New acetone/New total = .5

---> New acetone = Old acetone + acetone added = 10 + x

---> New total = old total + acetone added = 30 + x

(10 + x)/(30 + x) = .5
-------> 15 + .5x = 10 + x -------> 5 = .5x ---------> x = 10

Answer: D

gracie · Answer

let x=ounces of acetone to be added
10+x=.5(30+x)
x=10
C

viveknegi · Answer

How does 0.5 come? Please explain this point.

Posted from my mobile device

pushpitkc · Answer

Hi  viveknegi

The total concentration of the acetone must be 50% of the total solution.

Currently, we have 10 ounces of acetone and 30 ounces of the solution.
If we were to add x ounces of pure acetone to the solution, acetone will
be  \frac{1}{2}  or  0.5  of the total solution.

That's the reason  gracie  has formed the equation: 10+x = 0.5(30 + x)

Hope this helps you!

jp28 · Answer

A= 10 oz.
W= 20 oz.
Total = 30 oz.

If A is to equal 50% then....
 A + x = W
 10 + x = 20
 x = 10

Ans = C

generis · Answer

For mixture problems, this weighted average formula works well:

(% A)(Vol A)+ (% B)(Vol B) = (% A+B)(Vol A+B)

% = concentration of a substance or that substance as a fraction of the whole

A = current solution, acetone =  \frac{1}{3}  
A's volume = 30
B = solution to be added, acetone = 100% = 1
B's volume = x
Resultant solution (A+B), acetone:  \frac{1}{2} 
Vol of (A+B) = (30 + x)

(\frac{1}{3})*(30) + 1*x = \frac{1}{2}*(30+x) 
 10 + x = 15 + \frac{1}{2}x 
 \frac{1}{2}x=5 
 x = 10

She needs 10 ounces of pure acetone

Answer C

Funsho84 · Answer

Concentration 1 * Volume 1 = Conentration 2 * Volume 2 => C1*V1 = C2*V2

1/3*30 = 1/2*V2

V2= 20

Hence 10 ounces were added

Answer C

abhinashgc · Answer

Given:
Total mix(water+acceton)=30

Acceton=10.

So water content:30-10=20

After adding x acceton Ration become 50:50,no additional water.

So 10+x/20=1
Hence x=10

Sent from my iPad using  GMAT Club Forum mobile app

ScottTargetTestPrep · Answer

We can let n = the additional amount of acetone added and create the equation:

(10 + n)/(30 + n) = 1/2

2(10 + n) = 1(30 + n)

20 + 2n = 30 + n

n = 10

Answer: C

krish76 · Answer

currently,

10 ounce acetone so remaining 20 is water.
In order to make the mixture 50-50 additional acetone needed is 10

bumpbot · Answer

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A chemist is mixing a solution of acetone and water. She currently has

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