An investment of $2000 yields payments of $1200 in 3 years, $800 in 4 years, and $500 in 5 years. Thereafter, the investment is worthless. What constant rate of return r would the investment need to produce to yield the payments specified? The number r is called the internal rate of return on the investment. We can consider the investment as consisting of three parts, each part yielding one payment. The sum of the present values of the three parts must total $2000. This yields the equation 2000 = 1200e^-3r + 800e^-4r + 500e^-5r. Solve this equation to find the value of r.