The average cost of some books is $60.
If 8 of the books are now each $10 more and
4 of the books are now each $7 less,
the average cost of the books becomes $62.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
60 |
62 |
Total value |
60 u |
62 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 60 x 1 u
= 60 u
Increase in the cost after 8 books are now each $10 more and 4 books are now each $7 less
= 8 x 10 - 4 x 7
= 80 - 28
= $52
Total cost of books after 8 books are now each $10 more and 4 books are now each $7 less
= 60 u + 52
Total cost of books in the end
= 62 x 1 u
= 62 u
62 u = 60 u + 52
62 u - 60 u = 52
2 u = 52
1 u = 52 ÷ 2 = 26
Number of books in the end
= 1 u
= 26
Answer(s): 26