The average cost of some books is $52.
When another 7 books are added,
the total cost increases by $320.
The average cost becomes $50.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 7 |
Value |
52 |
50 |
Total value |
52 u |
50 u + 350 |
Number of books at first = 1 u
Number of books in the end = 1 u + 7
Total cost of books at first
= 1 u x 52
= 52 u
Total cost of the books in the end
= 50 x (1 u + 7)
= 50 u + 350
52 u + 320 = 50 u + 350
52 u - 50 u = 350 - 320
2 u = 30
1 u = 30 ÷ 2 = 15
Number of books in the end
= 1 u + 7
= 15 + 7
= 22
Answer(s): 22