Question

Counted a total of 40 white cars and yellow cars there were 9 times as many as white cars as yellow cars. how many white cars did he count show your work

Answer 1

Let W = number of white cars, and Y = number of yellow cars.
There were 9 times as many white cars as yellow cars. This means that the number of white cars was 9 times more than the number of yellow cars. This can be translated by the expression:
9Y = W
The person counted  40 cars in total:
W + Y = 40

So we get the system:
$\left \{ {{W+Y=40} \atop {9Y=W}} \right.$

In the first equation, we multiply by 9:
9W + 9Y = 360
In the second equation:
9Y= W
W-9Y = 0

Then we add the first with the second equation:
9W + 9Y + W - 9Y = 360
10 W = 360
W = 36

So He counted 36 white cars.

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