Hi Awli,

This question can be solved Algebraically or by TESTing VALUES. Here's how to TEST VALUES:

We're told that Cream costs twice as much as Skim Milk.

M = cost of Skim Milk = $2
C = cost of Cream = $4

We're told that a certain brand of milk is 1/4 cream and 3/4 skim milk. In real simple terms, that means for every "part" of cream there are 3 "parts" of skim milk.

Brand milk =
(1 part cream)($4) = $4
(3 parts skim milk)($2) = $6
Total price = $4 + $6 = $10

The question asks for the part of the price that is due to the CREAM.

Cream = $4
Total = $10
$4/$10 = 4/10 = 2/5

Final Answer:

GMAT assassins aren't born, they're made,
Rich
_________________

Thank you very much!

Hi Awli,

I'm glad that you found the explanation helpful. I mentioned that this question could also be solved with Algebra, so here's that approach:

We're told that Cream costs twice as much as Skim Milk.

P = price of skim milk
2P = price of cream

We're told that a certain brand of milk is 1/4 cream and 3/4 skim milk:

X = total ounces of milk

(1/4)(X)(2P) = the part of the cost that is cream
(3/4)(X)(P) = the part of the cost that is skim milk

Cost of Milk =
(1/4)(X)(2P) + (3/4)(X)(P) =
(1/2)(XP) + (3/4)(XP) =
(5/4)(XP)

The question asks what fraction of the cost was from the cream:

[(1/2)(XP)]/[(5/4)(XP)]

Cancel out the XPs...

(1/2)/(5/4)

Multiply the numerator and denominator by 4....

2/5

Final Answer:

GMAT assassins aren't born, they're made,
Rich
_________________

Thank you again EMPOWERgmatRichC !

Ratio of Cream:Milk = 1:3

3 portions of milk will cost 3x
1portion of cream will cost 2x

So 2x/(2x+3x)
2/5

Let Cream = C and Skim milk = S
Given that C = 2S
Let there be 4 liters of milk => 1 liter is cream and 3 liters are skim milk.

Let cost of skim milk = $10 => Cream = $20.
Total price = 1*$20 + 3*$10
= 50
Hence proportion of cream = 20/50
=2/5
Hence option (C).

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Let the price of milk = 1, then the price of cream = 2

Cost of milk in brand \(= 1 * \frac{3}{4} = \frac{3}{4}\)

Cost of cream in brand \(= 2 * \frac{1}{4} = \frac{1}{2}\)

Total cost \(= \frac{1}{2} + \frac{3}{4} = \frac{5}{4}\)

Required fraction\(= \frac{\frac{1}{2}}{\frac{5}{4}} = \frac{2}{5}\)

Answer = C

with no c, let total cost=4s
c=2s
with 1/4 c, total cost is 3s+2s=5s
c fraction of total cost=2s/5s=2/5

Lets assume total quantity be 100 units.

Cream = 25 units, Skim milk = 75 units

lets say skim milk cost is 1/unit, then cream = 2 per unit

total cost = 25*2+75 = 125

ratio = 50/125 = 2/5