ulm wrote:
At 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.
Target question: How many of the pets are dogs? Given: 1/3 of pets are dogs & 1/5 of pets are birds Let T = TOTAL number of pets.
So,
T/3 = number of dogsAnd T/5 = number of birds
Statement 1: There are 30 birds at the pet shop So, T/5 = 30
This means that T = 150, which means
T/3 = 50 (i.e., there are 50 dogs)
Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: There are 20 more dogs than birds at the pet shop. In other words, (# of birds) + 20 = # of dogs
We can now write: T/5 + 20 = T/3
IMPORTANT: We
could solve this equation for T, but we're not going to waste time doing so. We need only recognize that we
could solve the equation for T, which means
we can definitely find the value of T/3 (the number of dogs)Since we can answer the
target question with certainty, statement 2 is SUFFICIENT
Answer: D
Cheers,
Brent