The average cost of some books is $22.
When another 8 books are added,
the total cost increases by $130.
The average cost becomes $20.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 8 |
Value |
22 |
20 |
Total value |
22 u |
20 u + 160 |
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 22
= 22 u
Total cost of the books in the end
= 20 x (1 u + 8)
= 20 u + 160
22 u + 130 = 20 u + 160
22 u - 20 u = 160 - 130
2 u = 30
1 u = 30 ÷ 2 = 15
Number of books in the end
= 1 u + 8
= 15 + 8
= 23
Answer(s): 23