Question

The doubling time of the balance for a money market certificate of deposit (cd) is 25 years. by what factor does it grow in 40 years?

Answer 1

If the balance in a money market certificate of deposit doubles in 25 years then it has grown by 200%. For 40 years, that is 15 years more than the 25 so 15/25=0.6 x 200=120 %. Then a  weighted average of 25 x 200 and 15 x 120 gives 170% average growth.