The average cost of some books is $75.
When another 8 books are added,
the total cost increases by $150.
The average cost becomes $60.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 8 |
Value |
75 |
60 |
Total value |
75 u |
60 u + 480 |
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 75
= 75 u
Total cost of the books in the end
= 60 x (1 u + 8)
= 60 u + 480
75 u + 150 = 60 u + 480
75 u - 60 u = 480 - 150
15 u = 330
1 u = 330 ÷ 15 = 22
Number of books in the end
= 1 u + 8
= 22 + 8
= 30
Answer(s): 30