2012-05-01 09:00:09

If the ratio of cats to dogs in a certain pet stores is 7:3 and half the animals in the store are either dogs or cats, what percentage of animals in the store are cats?

(A) 15%
(B) 30%
(C) 35%
(D) 55%
(E) 70%

The correct answer is C

Explanation: If half the animals in the store are either dogs or cats, then the 7:3 ratio of cats to dogs only applies to half of the store. 7:3 is a part-to-part ratio, but the question will require you to make it a part-to-whole ratio by adding the two parts together. Thus, the ratio of cats to cats or dogs in the store is 7:10 (from 7 + 3 = 10), meaning that 70% of the cats/dogs sold in the store are cats. Since that is half the store only,  the correct answer is 70% of half or 70% of 50%, which is 35%, or choice C.

This could also be found by assuming there are 100 total animals sold in the store. That would mean that 50 animals are either cats or dogs, and that 7/10 of 50 is the number of cats in the store. 7/10 of 50 is 35.