To save for their retirement, a couple deposits $4000 in

an account that pays 5.9% annual interest compounded
quarterly. What will be the value of their investment
after 20 yr?

1 answer

What is 4000(1+.059/4)^80 ?

(that would take them through about 1/4 of the first year of their retirement)

I hope you mean that they deposit $4000 every quarter year for 20 years.

if that is the case they would have

4000 (1 + .059/4)^80 - 1)/(.059/4)
= $603 782.77

(that's more like it)