Question: A man puts $10 in the bank for his son on each of his birthdays from the first to the twentieth inclusive. If the money accumlates at 3% compound interest, what is the toatl value on the son's twenty-first birthday? My answer is like this: a = 10, r = 1.03, n = 20 Total value = a * (r^n - 1) / (r - 1) = 10 * (1.03^20 - 1) / 0.03 = 269 (approx.) But the answer is 276, what is the problem? The $10 of the first year will immediately be counted for interest or not? And also how to define the final year, it is the 20th year or the 21st year?