Question

Jamal and his friends are conducting a car wash to raise money for a school play. Over the first weekend they raised $336.00 which was 80% of what they set out to earn. If they collect $21 for each car they wash, how many more cars must they wash?

Answer 1

What hey want to collect is X

80% of X = $ 336

Amount raised by friends 1s $336.00

1% of X = $ 336/80 = $ 42

100% 0f X = $ 42 x 100 = $ 420

Amount needed = $ 420 - 336 = $ 84

Earnings for each car washed = $ 21

Number of cars needed to wash is 84/21 = 4

Answer 2

Let's call
`x` the desired amount. We know that the 80% of x is 336. Since we compute the 80% of something by multiplying it by 0.8, we have

`0.8x = 336 \implies x = (336)/(0.8) = 420`.

So, they still need to collect

`420-336 = 84` dollars.

At a rate of 21 dollar per car, they still have to wash

`(84)/(21) = 4` cars.