The average cost of some books is $46.
When another 5 books are added,
the total cost increases by $110.
The average cost becomes $40.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 5 |
Value |
46 |
40 |
Total value |
46 u |
40 u + 200 |
Number of books at first = 1 u
Number of books in the end = 1 u + 5
Total cost of books at first
= 1 u x 46
= 46 u
Total cost of the books in the end
= 40 x (1 u + 5)
= 40 u + 200
46 u + 110 = 40 u + 200
46 u - 40 u = 200 - 110
6 u = 90
1 u = 90 ÷ 6 = 15
Number of books in the end
= 1 u + 5
= 15 + 5
= 20
Answer(s): 20