Q470. This is one of a series of problems (469, 471, 472, 473, 474, 475, 476, 477, 478) relating to the same fictional case: The community of Ourville which is considering some options for creating parks to enhance the quality of life of local residents. The amounts are expressed in simple numbers – e.g., $100 – which you can assume to be referring to realistic amounts – e.g., hundreds of thousands.
One part of the staff report talks about discounting. A resident asks "where do discount rates come from?" Your (BRIEF) answer: