The average cost of some books is $50.
If 8 of the books are now each $13 more and
3 of the books are now each $8 less,
the average cost of the books becomes $52.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
50 |
52 |
Total value |
50 u |
52 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 50 x 1 u
= 50 u
Increase in the cost after 8 books are now each $13 more and 3 books are now each $8 less
= 8 x 13 - 3 x 8
= 104 - 24
= $80
Total cost of books after 8 books are now each $13 more and 3 books are now each $8 less
= 50 u + 80
Total cost of books in the end
= 52 x 1 u
= 52 u
52 u = 50 u + 80
52 u - 50 u = 80
2 u = 80
1 u = 80 ÷ 2 = 40
Number of books in the end
= 1 u
= 40
Answer(s): 40