b1. F = Pert , which assumes continuous compounding, says that the Future value (F) of an amount (P) invested today at an annual rate (r, expressed as a decimal) for the time (t, expressed in years) is given by the function. e is usually a key on a scientific calculator or it may be considered a constant approximately equal to 2.7183. EXAMPLE: If you invested $100 at the annual rate of 5 1/2% for 6 years and 3 months you would get back (at the end of the time), F = $100e(0.055)(6.25) = $100e(0.3438) = $100(1.4102) = $141.02. YOUR PROBLEM: Suppose you put $60000 in a savings account paying 4% per annum for 30 years for your retirement. What should your retirement account be worth after 30 years