Can anyone solve this problem for k please: $100/k = $100/k X [1-1/(1+k)¹⁰] ? It is an annuity vs. perpetuity problem. The annuity side is on the left and the perpituity side is on the right. Here is the question: You have just read an advertisement stating, "Pay us $100 a year for the next ten years and we will pay you $100 a year thereafter in perpetuity." If this is a fair deal, what is the implied rate of interest. That is all we are given. k is the interest rate we need to find. Thanks