Math 110 Course Resources - Compound Interest Course Packet on solving for an unknown length of time with discrete compounding of interest How long will it take for $2,000 to grow to $9,000 if the investment earns an interest rate of 6% per year compounded semiannually (i.e., 2 times a year). Exact length of time (without using a calculator), t = years Length of time, rounded to 2 decimal places = years