Question

If you borrow $15,000 from your dad for college and you agree to pay him $25,000 back at 8% compound interest per year. How many years do you think you have to do this? In other words, given the amounts and the interest rate, what is the number of years?

Answer 1

so
25,000 = 15,000(1.08)^n
5/3 = 1.08^n
log(5/3) = n log 1.08
n = log(5/3) / log 1.08 = appr 6.6 years

Answer 2

Holy Waa!!
Your dad is a loan shark.... call the cops!