Jack spent half of his weekly allowance on video games. To earn more money his parents let him wash the car for $6. What is his weekly allowance if he ended with $15?

Answer 1

Work backward. If he has $15, he had 15 - 6 = $9 before washing the car.

If $9 is the half he didn't spend, he spent the other $9 on video games.

9 + 9 = $18

Answer 2

Let X = Jack's weekly allowance

If he spent 1/2 of it on video game, then he had 1/2 of it left (1/2)X

After he earned $6 for cleaning the car, he had $15.

So,

(1/2)X + 6 = 15

(1/2)X = 9

X = 18

 

His weekly allowance is then $18.