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 3 strokes ?	Pick one: A) 15/16 B) 7/8 C) 1/4 D) 1/8 E) 1/16
Left After 1st stroke = 1/2   Left After 2nd stroke = 1/2 * 1/2 = 1/4   Left After 3rd stroke = 1/2 * 1/4 = 1/8   So removed = 1- 1/8 = 7/8=7/8
<result>B</result>
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 3 strokes ?