The average cost of some books is $32.
If 5 of the books are now each $10 more,
the average cost of the books becomes $37.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
32 |
37 |
Total value |
32 u |
37 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 32 x 1 u
= 32 u
Total cost of books in the end
= 37 x 1 u
= 37 u
Increase in the cost when 5 books are now each $10 more
= 5 x 10
= $50
Total cost of books after 5 books are now each $10 more
= 32 u + 50
37 u = 32 u + 50
37 u - 32 u = 50
5 u = 50
1 u = 50 ÷ 5 = 10
Number of books in the end
= 1 u
= 10
Answer(s): 10