Let w bet the number of white cars and y the numbers of yellow cars. "Rafael counted a total of 40 white and yellow cars" So w+y = 40. "There were 9 times as many white cars as yellow cars" So 9Y = W
We get the system: w+y=40 (1) 9y=w (2)
In equation (1), let's replace w by it's value from equation (2) since w=9y. We get: 9y+y = 40 10y=40 y=4 So there's 4 yellow cars.
In equation (1), let's replace y by it's value w+4=40 w=40-4 w=36
Rafael counted 36 white cars.
You can re-check your answer: 4+36=40 (w+y=40) 9*4=36 (9y=w) The answer has been approved.
That's the simplest form of 15/35. You can use 3/7 to get other equivalent fractions by multiplying the numerator and denominator by the same number. Other examples are 9/21, 6/14, and 12/28. Hope this helps!