Data Sufficiency

Aishwarya1204 wrote:At a certain picnic, each of the the guests was served either a single scoop or a double scoop of ice cream. How many of the guests were served a double scoop of ice cream?

1) At the picnic, 60 percent of the guests were served a double scoop of ice cream.
2) A total of 120 scoops of ice cream were served to all the guests at that picnic.

Let the no. of people who were served single scoop of ice cream = S
and the no. of people who were served double scoop of ice cream = D

(1) At the picnic, 60 percent of the guests were served a double scoop of ice-cream.
Then S : D = 40 : 60 = 2 : 3, but using this we cannot find the value of D; NOT sufficient.

(2) A total of 120 scoops of ice-cream were served to all the guests at the picnic.
S + 2D = 120, which is again NOT sufficient to find D.

Combining (1) and (2), we have 2 equation: S = 2D/3 and S + 2D = 120
Solving we get, 2D/3 + 2D = 120; which can be solved for D; SUFFICIENT.

The correct answer is C.