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another data sufficiency question

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another data sufficiency question

by nickhar130 » Fri Jan 07, 2011 3:46 pm
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 then birds at the pet shop.

How do i solve with the 2nd information given by itself. Please explain.
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by anshumishra » Fri Jan 07, 2011 4:00 pm
nickhar130 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 then birds at the pet shop.

How do i solve with the 2nd information given by itself. Please explain.
Let there are a total of x pets.
x/3 -> dogs = ?
x/5 -> birds
So, if we know x, we can calculate x/3, so question stem is , x = ?

Statement 1:
x/5 = 30 - Sufficient
(=> x = 150 --- You don't need to calculate it, as long as you know you can find it.)

Statement 2:
x/3 - x/5 = 20 [STOP, RIGHT HERE...YOU DONT NEED TO CALCULATE X. YOU HAVE AN EQUATION FOR X IN ONE DEGREE, SO IT IS SUFFICIENT]
I AM SHOWING IT HERE, AS THAT WAS YOUR QUESTION
=> (5x-3x)/15 = 200
=> x = 15*200/2 = 150

Hence, D
Thanks
Anshu

(Every mistake is a lesson learned )
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