The average cost of some books is $46.
When another 4 books are added,
the total cost increases by $100.
The average cost becomes $40.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 4 |
Value |
46 |
40 |
Total value |
46 u |
40 u + 160 |
Number of books at first = 1 u
Number of books in the end = 1 u + 4
Total cost of books at first
= 1 u x 46
= 46 u
Total cost of the books in the end
= 40 x (1 u + 4)
= 40 u + 160
46 u + 100 = 40 u + 160
46 u - 40 u = 160 - 100
6 u = 60
1 u = 60 ÷ 6 = 10
Number of books in the end
= 1 u + 4
= 10 + 4
= 14
Answer(s): 14