The average cost of some books is $40.
If 8 of the books are now each $8 more and
3 of the books are now each $4 less,
the average cost of the books becomes $42.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
40 |
42 |
Total value |
40 u |
42 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 40 x 1 u
= 40 u
Increase in the cost after 8 books are now each $8 more and 3 books are now each $4 less
= 8 x 8 - 3 x 4
= 64 - 12
= $52
Total cost of books after 8 books are now each $8 more and 3 books are now each $4 less
= 40 u + 52
Total cost of books in the end
= 42 x 1 u
= 42 u
42 u = 40 u + 52
42 u - 40 u = 52
2 u = 52
1 u = 52 ÷ 2 = 26
Number of books in the end
= 1 u
= 26
Answer(s): 26