Data Sufficiency

At a certain pet shop, 1/3 of pets are dogs & 1/5 of 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.

OA D

Explanation plz

Drishti wrote:At a certain pet shop, 1/3 of pets are dogs & 1/5 of 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.

Question : Number of Dogs = ?

Let the total number of pets be = P

Given, (1/3)P = Dogs

and (1/5)P = Birds

We can find the number of dogs if we can find the value of P

Statement 1) Number of birds = 30

=> (1/5)P = 30 => P = 150, therefore Dog = 150/3 = 50

SUFFICIENT

Statement 2) 20 more Dogs than Birds

=> Dogs = Birds + 20

=> (1/3)P = (1/5)P + 20

i.e. (2/15)P = 20
i.e. P = 150 therefore Dog = = 150/3 = 50

SUFFICIENT

Answer: Option D

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Drishti wrote:At a certain pet shop, 1/3 of pets are dogs & 1/5 of 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.