A principal earns 7% per year simple interest. How long will it take for the future value to quadruple?

Answer 1

consider $1

to obtain 4 times the $1, we need $3 in interest

3 = 1(.07)(t)
t = 3/.07 = appr 42.9 years

check:
consider $100
interest at 7% for 42.9 years
= 100(.07)(42.9 = 300.3
so add that to the 100 we started with, we get 400.3