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