so 5 red cars
1/3 of all cars are red
therefor
5=1/3 of all cars
'of' means multply
5=1/3 times all cars
multiply both sides by 3
15=all cars
how many are left
basically how many are NOT red
15=all
red=5
all-red=others
15-5=others=10
10 cars are left
