In this paper, an investment problem is investigated in terms of elementary algebra, recurrence relations, functions, and calculus at high school level. The problem comes down to understanding the behaviour of a function associated with the problem and, in particular, to finding the zero of the function. A wider purpose is not only to formulate the problem mathematically and to make necessary calculations, but to think on a wider front, and to seek insight and mathematical modes of thinking in relation to general investment strategy.