Solve the following word problem below, show work, use a table

Question

It takes a man 5 hrs. to wash and wax his car. If his son helps him, it only takes 3 hours. How long would it take the son, working alone, to wash and wax the car?

Answer 1

The man takes 5 hrs.

Let x = time it takes for son working alone.

Working together, they will take 3 hours.

Now the rational equation is 1/5 + 1/x = 1/3

(x + 5)/5x = 1/3

Cross multiplication.

3x + 15 = 5x

5x - 3x = 15

2x =  15

x = 15/2

x = 7.5 hours.

The son takes 7.5 hours working alone to wash and wax the car.