Compound Interest Formulas The interest of a compound interest investment or loan can be computed with the formula I = A P (where A is given below). The end amount of a compound interest investment or loan can be computed with the formula nt P(1 + 7 ) m n |A = P(1- Use these formulas to evaluate the amounts indicated below. Let P = $6, 800, r = 8.2%, n= 12, and t = 5 years. Determine the interest, I, at the end of 5 years. Interest = $ dollars Let P = $5, 100, r = 12.3%, n = 2, and t = 11 years. Determine the total end amount, A, at the end of 11 years. End Amount = $ dollars