The average cost of some books is $50.
When a book that costs $72 is added,
the average cost of the books becomes $52.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
50 |
52 |
Total value |
50 u |
52 u + 52 |
Number of books at first = 1 u
Number of books in the end = 1 u + 1
Total cost of the books at first
= 50 x 1 u
= 50 u
Total cost of books in the end
= 50 u + 72
Total cost of books in the end
= 52 x (1 u + 1)
= 52 u + 52
50 u + 72 = 52 u + 52
52 u - 50 u = 72 - 52
2 u = 20
1 u = 20 ÷ 2 = 10
Number of books in the end
= 1 u + 1
= 10 + 1
= 11
Answer(s): 11