The average cost of some books is $35.
If 9 of the books are now each $12 more and
5 of the books are now each $8 less,
the average cost of the books becomes $37.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
35 |
37 |
Total value |
35 u |
37 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 35 x 1 u
= 35 u
Increase in the cost after 9 books are now each $12 more and 5 books are now each $8 less
= 9 x 12 - 5 x 8
= 108 - 40
= $68
Total cost of books after 9 books are now each $12 more and 5 books are now each $8 less
= 35 u + 68
Total cost of books in the end
= 37 x 1 u
= 37 u
37 u = 35 u + 68
37 u - 35 u = 68
2 u = 68
1 u = 68 ÷ 2 = 34
Number of books in the end
= 1 u
= 34
Answer(s): 34