A certain zoo has mammal and reptiles and birds, and no

[AAPL]

Magoosh

A certain zoo has mammal and reptiles and birds, and no other animals. The ratio of mammals to reptiles to birds is 11: 8:5. How many birds are in the zoo?

1) there are twelve more mammals in the zoo than there are reptiles.
2) if the zoo acquired 16 more mammals, the ratio of mammals to birds would be 3:1.

OA D

[Brent@GMATPrepNow]

Magoosh

A certain zoo has mammal and reptiles and birds, and no other animals. The ratio of mammals to reptiles to birds is 11: 8:5. How many birds are in the zoo?

1) there are twelve more mammals in the zoo than there are reptiles.
2) if the zoo acquired 16 more mammals, the ratio of mammals to birds would be 3:1.

OA D

Target question: How many birds are in the zoo?

Given: The ratio of mammals to reptiles to birds is 11: 8:5.
Given this ratio, we could say that there are:
11x mammals
8x reptiles
5x birds
for some value of x.

Statement 1: there are twelve more mammals in the zoo than there are reptiles
We can write: number of mammals = number of reptiles + 12
Or we can write: 11x = 8x + 12
Solve to get x = 4
Once we know the value of x, we can see that the number of birds = 5x = (5)(4) = 20
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: if the zoo acquired 16 more mammals, the ratio of mammals to birds would be 3:1
So, (current number of mammals + 16)/(current number birds) = 3/1
Or we can write: (11x +16)/5x = 3/1
Cross multiply to get: 11x + 16 = 15x
Solve, to get x = 4
Once we know the value of x, we can see that the number of birds = 5x = (5)(4) = 20
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer = D

Cheers,
Brent