swerve wrote:Salad dressing A is made up of 30% vinegar and 70% oil, and salad dressing B contains 10% vinegar and 90% oil. If the 2 dressing are combined to produce a salad dressing that is 15% vinegar, dressing A comprises what % of the new dressing?
A. 15%
B. 20%
C. 25%
D. 40%
E. 55%
Vinegar in A = 30%.
Vinegar in B = 10%.
Vinegar in the MIXTURE of A and B = 15%.
To determine the ratio of A to B, use ALLIGATION -- a very efficient way to handle mixture problems.
Step 1: Plot the 3 percentages on a number line, with the percentages for A and B (30% and 10%) on the ends and the percentage for the mixture (15%) in the middle.
A 30----------15-----------10 B
Step 2: Calculate the distances between the percentages.
A 30----
15----15----
5----10 B
Step 3: Determine the ratio in the mixture.
The required ratio of A to B is equal to the RECIPROCAL of the distances in red.
A:B = 5:15 = 1:3.
Thus, of every 4 liters:
A = 1 liter.
B = 3 liters.
A/total = 1/4 = 25%.
The correct answer is
C.
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