algebra
posted by Beverly on .
A parent raises a child's allowance by 12% each year. If the allowance is $3.50 now, when will it reach $18?

18 = 3.5(1.12)^n
5.142857 = 1.12^n
take log of both sides and use log rules....
n = log 5.142857/log 1.12 = 14.45
so after 14 years the allowance will be below $18
but after 15 years it will be over $18