The average cost of some books is $55.
If 8 of the books are now each $14 more and
5 of the books are now each $8 less,
the average cost of the books becomes $58.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
55 |
58 |
Total value |
55 u |
58 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 55 x 1 u
= 55 u
Increase in the cost after 8 books are now each $14 more and 5 books are now each $8 less
= 8 x 14 - 5 x 8
= 112 - 40
= $72
Total cost of books after 8 books are now each $14 more and 5 books are now each $8 less
= 55 u + 72
Total cost of books in the end
= 58 x 1 u
= 58 u
58 u = 55 u + 72
58 u - 55 u = 72
3 u = 72
1 u = 72 ÷ 3 = 24
Number of books in the end
= 1 u
= 24
Answer(s): 24