Full question below:

Question

In a halloween party the judges eliminated 1/3 of the eligible contestants after every 20 minutes. If 135 contestants were present at the party, how many would still be eligible for a prize after 1 hour?

 

Choices:

a) 5

b) 15

c) 40

d) 60

 

Please help. I keep getting 0 but it's not in the choices. 

Answer 1

You aren't taking away 45 each time. You are taking away 1/3 of the new total each time.

 

(1/3)135 = 45

135 - 45 = 90

(1/3)90 = 30

Etc.

 

Or, 135(2/3)³ = 135(8/27) = 40

 

C