Answer: 24 books
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Explanation:
- N = number of books in the 3rd stack
- 2N = number of books in the 2nd stack, since there are twice as many books here.
- 2N+30 = add on 30 to the previous amount to get the number of books in the first stack
In other words,
- 1st stack = 2N+30
- 2nd stack = 2N
- 3rd stack = N
N is some positive whole number.
Add up all those expressions and set the sum equal to the 150 books total. Solve for N.
(1st stack) + (2nd stack) + (3rd stack) = total
(2N+30) + (2N) + (N) = 150
(2N+2N+N) + 30 = 150
5N + 30 = 150
5N = 150-30
5N = 120
N = 120/5
N = 24 which is the number of books in the 3rd stack
2N = 2*24 = 48 is the number of books in the 2nd stack.
2N+30 = 2*24+30 = 48+30 = 78 books in the 1st stack
Check:
1st+2nd+3rd = 78+48+24 = 150
The answer is confirmed.
