The average cost of some books is $50.
When another 8 books are added,
the total cost increases by $200.
The average cost becomes $40.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 8 |
Value |
50 |
40 |
Total value |
50 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 50
= 50 u
Total cost of the books in the end
= 40 x (1 u + 8)
= 40 u + 320
50 u + 200 = 40 u + 320
50 u - 40 u = 320 - 200
10 u = 120
1 u = 120 ÷ 10 = 12
Number of books in the end
= 1 u + 8
= 12 + 8
= 20
Answer(s): 20