The average cost of some books is $25.
If 8 of the books are now each $12 more and
3 of the books are now each $8 less,
the average cost of the books becomes $29.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
25 |
29 |
Total value |
25 u |
29 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 25 x 1 u
= 25 u
Increase in the cost after 8 books are now each $12 more and 3 books are now each $8 less
= 8 x 12 - 3 x 8
= 96 - 24
= $72
Total cost of books after 8 books are now each $12 more and 3 books are now each $8 less
= 25 u + 72
Total cost of books in the end
= 29 x 1 u
= 29 u
29 u = 25 u + 72
29 u - 25 u = 72
4 u = 72
1 u = 72 ÷ 4 = 18
Number of books in the end
= 1 u
= 18
Answer(s): 18