math
posted by miki .
3000 exercise books are arranged in 3 piles.The first pile has 10 more books than the second pile.The number of books in the second pile is twice the number of books in the third pile.How many books are there in the third pile?

Let x = # books in third pile, then second pile = 2x, and first pile = 2x + 10.
x + 2x + (2x+10) = 3000
Solve for x.