If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 5 strokes ?  Choose the most appropriate option.
A) 31 / 32  B) 7 / 8  C) 1 / 4  D) 1 / 8  E) 1 / 16

Rationale: left after 1 st stroke = 1 / 2 left after 2 nd stroke = 1 / 2 * 1 / 2 = 1 / 4 left after 3 rd stroke = 1 / 2 * 1 / 4 = 1 / 8 left after 4 th stroke = 1 / 2 * 1 / 8 = 1 / 16 left after 5 th stroke = 1 / 2 * 1 / 16 = 1 / 32 so removed = 1 - 1 / 32 = 31 / 32
Answer: A