Try this GRE Word Problems question [Difficulty level – Medium]

A restaurant opened today and planned to see 40 dozen pastries. Half of the pastries were sold by 12:00 pm, and 80 percent of the remaining pastries were sold between 12:00 pm and 5:00 pm. How many dozen pastries had not been sold by 5:00 pm?

(A) 1
(B) 2
(C) 3
(D) 4
(E) 5

Here is the solution:

Since half of the 40 dozen pastries were sold by 12:00 pm, then 20 dozen pastries were left to be sold. Because 80 percent of those 20 were sold, 100 – 80 = 20 percent of them or 20(0.20) = 4 dozen pastries had not been sold when the restaurant closed.