Answer:
598 books
Explanation:
Let x be the number of books in the 3rd pile. We will have then:
1st pile: 2x + 10
2nd pile: 2x
3rd pile: x
3000 = (2x + 10) + (2x) + (x)
3000 = 5x + 10
3000 - 10 = 5x
2990 = 5x
2990/5 = x
x = 598 books in the third pile!
We can check that:
3000 = 2*598 + 10 + 2*598 + 598
3000 = 1196 + 10 + 1196 + 598
3000 = 3000 CHECK!