srivats212 wrote:

Could someone please help me out with the below problem:

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 4 strokes?

A. 15/16

B. 7/8

C. 1/4

D. 1/8

E. 1/16

This question is actually from the

OG 12th edition. Am not able to understand the explanation given in

OG for this problem. Could someone please explain in detail as to how to solve this

The best thing to do here is plug in

Assume that there is 16 units of air in the tank

first stroke = 1/2*16 = 8 ( we are left ith 8 now)

second stroke = 1/2*8 = 4( left ith 4 units now)

third stoke = 1/2*4 = 2( left with 2 units)

4th stroke = 1/2* 2 = 1 (left with 1 unit)

total units removed = 8+4+2+1 = 15

total unis in the tank at the begining = 16

thus its A . 15/16

Hope this helps