The average cost of some books is $35.
If 7 of the books are now each $9 more and
3 of the books are now each $5 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 7 books are now each $9 more and 3 books are now each $5 less
= 7 x 9 - 3 x 5
= 63 - 15
= $48
Total cost of books after 7 books are now each $9 more and 3 books are now each $5 less
= 35 u + 48
Total cost of books in the end
= 37 x 1 u
= 37 u
37 u = 35 u + 48
37 u - 35 u = 48
2 u = 48
1 u = 48 ÷ 2 = 24
Number of books in the end
= 1 u
= 24
Answer(s): 24