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.

5 years

Step-by-step 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