Data Sufficiency

At a certain picnic, each of 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 the picnic.

sachindia wrote:At a certain picnic, each of 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 the picnic.

Statement 1: 60% of the guests were served a double scoop
Let the number of guests = 10, implying that 6 guests are served 2 scoops each and that 4 guests are served 1 scoop each.
Number of scoops served to the double-scoop guests = 6*2 = 12.
Number of scoops served to the single-scoop guests = 4*1 = 4.
Thus, of every 16 scoops, 12 are served to the double-scoop guests:
12/16 = 3/4.
No way to determine the number of double-scoop guests.
INSUFFICIENT.

Statement 2: total scoops = 120
No way to determine the number of double-scoop guests.
INSUFFICIENT.

Statements 1 and 2 combined:
Number of scoops served to the double-scoop guests = (3/4)*120 = 90.
Since each double-scoop guest receives 2 scoops, the number of double-scoop guests = 90/2 = 45.
SUFFICIENT.

The correct answer is C.

Thanks a lot, Mitch!!