Posted by **Josie** on Wednesday, March 6, 2013 at 7:37pm.

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=18-Y. whats next??

thank you for helping if u can.

- algebra -
**Reiny**, Wednesday, March 6, 2013 at 8:59pm
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 = 18-y

5000x + 3000y = 30(2000)

divide by 1000

5x + 3y = 60

sub in your first part

5(18-y) + 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

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