AAPL wrote:GMAT Prep
In a certain pet shop, 1/3 of the pets are dogs and 1/5 of the pets are birds. How many of the pets are dogs?
1) There are 30 birds at the pet shop.
2) There are 20 more dogs than birds at the pet shop.
Alternate approach:
To determine the ratio of birds to dogs, plug in a TEST VALUE for the total number of pets.
Let b = the number of birds and d = the number of dogs.
Let the test value for the total number of pets = the LCM of 3 and 5 = 15.
Since 1/5 are birds, b = 1/5 * 15 = 3.
Since 1/3 are dogs, d = 1/3 * 15 = 5.
Thus:
b/d = 3/5.
Statement 1: There are 30 birds at the pet shop
Since b/d = 3/5 = 30/50, b=30 and d=50.
SUFFICIENT.
Statement 2: There are 20 more dogs than birds at the pet shop
The values yielded by statement 1 -- b=30 and d=50 -- are the only values for b and d such that b/d = 3/5 and d=b+20.
SUFFICIENT.
The correct answer is
D.
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