The average cost of some books is $37.
If 4 of the books are now each $13 more,
the average cost of the books becomes $39.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
37 |
39 |
Total value |
37 u |
39 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 37 x 1 u
= 37 u
Total cost of books in the end
= 39 x 1 u
= 39 u
Increase in the cost when 4 books are now each $13 more
= 4 x 13
= $52
Total cost of books after 4 books are now each $13 more
= 37 u + 52
39 u = 37 u + 52
39 u - 37 u = 52
2 u = 52
1 u = 52 ÷ 2 = 26
Number of books in the end
= 1 u
= 26
Answer(s): 26