Question

A speaker was so boring that one-half of the audience left after a few minutes. Five minutes later, one-third of the remaining audience left. Ten minutes later, one-fourth of those remaining left, leaving only nine people in the audience. How many people were in the audience at the beginning of the lecture.

Answer 1

x = people in audience
1/2 x = left 1st
1/3 (1/2 x) = 1/6 x = left next
1/4 (1/3)(1/2)x = 1/24 x = left last

x - (1/2 x + 1/6 x + 1/24 x) = 9

Solve for x