The average cost of some books is $55.
If 4 of the books are now each $14 more and
2 of the books are now each $4 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 4 books are now each $14 more and 2 books are now each $4 less
= 4 x 14 - 2 x 4
= 56 - 8
= $48
Total cost of books after 4 books are now each $14 more and 2 books are now each $4 less
= 55 u + 48
Total cost of books in the end
= 58 x 1 u
= 58 u
58 u = 55 u + 48
58 u - 55 u = 48
3 u = 48
1 u = 48 ÷ 3 = 16
Number of books in the end
= 1 u
= 16
Answer(s): 16