David charges $4 to wash all the windows of a car, inside and out. The amount of money he earns washing the windows must end in one of what digits? Why? List all the possible digits.

The possible digits are : 0, 2, 6, 4, 8

Step-by-step explanation:

Money charged by David to wash the windows of a car = $4

Let total number of cars he washed be x

Now, Total money earned by washing windows of a car = Money charged for washing all windows of one car * Total number of cars washed

⇒ Total money earned = 4 * x

So, the amount will always end in the digits which comes at the end of multiples of 4 because the amount will be always in the multiples of 4

⇒ 4 * 1 = 4, 4 * 2 = 8, 4 * 3 = 12, 4 * 4 = 16, 4 * 5 = 20 ...

So, the possible digits are : 0, 2, 6, 4, 8