SOLUTION: A parent increases a child’s allowance by 12% each year . If the allowance is $5 now , when will it reach $20?

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Question 1155676: A parent increases a child’s allowance by 12% each year . If the allowance is $5 now , when will it reach $20?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
20=5(1.12)^t, where t is number of years. This is the interest formula and exponential as well.
4=1.12^t
ln 4=t ln 1.12
t=ln4/ln 1.12
=12.23 years. It will be in the 13th year.