Mr. smith junior wishes to buy a used car in a year's time when he turns 18, and he is willing to spend $5,000. he plans to work part-time and put all his monthly earnings into a bank account that will pay 0.5% interest per month. how much must he earn per month in order to be able to purchase the car in one year's time? the correct answer is $405.33 and not $430.33. how do we get to this?