The average cost of some books is $54.
When another 8 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 + 8 |
Value |
54 |
40 |
Total value |
54 u |
40 u + 320 |
Number of books at first = 1 u
Number of books in the end = 1 u + 8
Total cost of books at first
= 1 u x 54
= 54 u
Total cost of the books in the end
= 40 x (1 u + 8)
= 40 u + 320
54 u + 110 = 40 u + 320
54 u - 40 u = 320 - 110
14 u = 210
1 u = 210 ÷ 14 = 15
Number of books in the end
= 1 u + 8
= 15 + 8
= 23
Answer(s): 23