algebra
posted by Josie .
A shipment of 18 cars, some weighting 3000lbs a piece, and the others weighing 5000 lbs each, has a total weight of 30 tons. Find the number of each kind of car.
I start of saying X+Y = 18. THen I turn that into X=18Y. whats next??
thank you for helping if u can.

you have to define your x and y
let the number of heavy cars be x
let the number of lighter cars be y
so, ok, at
x+y = 18
x = 18y
5000x + 3000y = 30(2000)
divide by 1000
5x + 3y = 60
sub in your first part
5(18y) + 3y = 60
90  5y + 3y = 60
2y = 30
y = 15
There were 15 of the lighter cars, and 3 of the heavier cars
check:
15(3000) + 3(5000) = 60000 pounds = 30 tons