BTGmoderatorLU wrote:At Pete's Pet Shop, 35 cups of birdseed are used every 7 days to feed 15 parakeets. How many cups of bird seed would be required to feed 9 parakeets for 12 days?

A. 32
B. 36
C. 39
D. 42
E. 45

The OA is B.

Per cup consumption = 7*15/35 which will be constant
so: 7 * 15/35 = 9*12/x => x=36. Hence the correct answer is B.

Please, can anyone explain another way to solve this PS question? Thanks.

35 cups of seed in 7 days = 5 cups per day.
5 cups per day divided by 15 birds = 1/3 cup per bird per day.

Therefore, 9 birds require 9*(1/3) = 3 cups of seed per day.
And over a 12-day period, those 9 birds require 12*3 = 36 cups of seed.

The correct answer is choice B.

Hope this helps.

Hi All,

We're told that 35 cups of birdseed are used every 7 days to feed 15 parakeets. We're asked for the number of cups of birdseed needed to feed 9 parakeets for 12 days. In these types of rate questions, it often helps to think in terms of the 'totals' involved and then work 'backwards' from that information.

Here, we start by feeding 15 parakeets for 7 days; that is (15)(7) = 105 parakeet-days of food. The 35 cups of birdseed leads to that result, so we can determine what ONE cup of birdseed is equivalent to...

(105 parakeet-days)/(35 cups) = 3 parakeet-days of food from 1 cup

Thus, with 1 cup of birdseed, we could feed...
1 parakeet for 3 days
3 parakeets for 1 day
2 parakeets for 1.5 days
etc.

We're asked for the number of cups needed to feed 9 parakeets for 12 days. That would be (9)(12) = 108 parakeet-days of food needed and since 1 cup = 3 parakeet-days of food....
108/3 = 36 cups needed

Final Answer: B

GMAT assassins aren't born, they're made,
Rich