The methods for calculating returns on investments are taught to undergraduate level business students. In this paper, the authors demonstrate how such calculations are within the scope of senior school students of mathematics. In providing this demonstration the authors hope to give teachers and students alike an illustration of the power and the utility of the mathematics they are working with in the senior school classroom which in turn can be a source of motivation for them. This paper bridges the gap between calculations of rates of return and the senior mathematics syllabus. It defines precisely what they mean by a rate of return on an investment and describes how a business might determine a rate of return it requires before making an investment or before undertaking a new venture. The authors provide a thought-provoking challenge to capable senior students. (Contains 2 tables, 2 figures and 4 footnotes.)