Question

A parent increases a child's allowance by 15 % each year. If the allowance is now $9, about how many years will it take for it to double? Use the equation 18 9(1.15)^x. Round to the nearest year.

Answer 1

5 years

Explanation:

18= 9(1.15)^x

Divide each side by 9

18/9= 9/9 *(1.15)^x

2 = 1.15 ^x

Take the log on each side

log (2) = log (1.15^x)

log 2 = x log 1.15

Divid each side by log (1.15)

log 2 / log 1.15 = x log 1.15/ log 1.15

log 2 / log 1.15 = x

4.959484455 = x

To the nearest year

5 years