The average cost of some books is $45.
If 8 of the books are now each $12 more and
5 of the books are now each $4 less,
the average cost of the books becomes $49.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
45 |
49 |
Total value |
45 u |
49 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 45 x 1 u
= 45 u
Increase in the cost after 8 books are now each $12 more and 5 books are now each $4 less
= 8 x 12 - 5 x 4
= 96 - 20
= $76
Total cost of books after 8 books are now each $12 more and 5 books are now each $4 less
= 45 u + 76
Total cost of books in the end
= 49 x 1 u
= 49 u
49 u = 45 u + 76
49 u - 45 u = 76
4 u = 76
1 u = 76 ÷ 4 = 19
Number of books in the end
= 1 u
= 19
Answer(s): 19