The average cost of some books is $50.
When a book that costs $83 is added,
the average cost of the books becomes $53.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
50 |
53 |
Total value |
50 u |
53 u + 53 |
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 + 83
Total cost of books in the end
= 53 x (1 u + 1)
= 53 u + 53
50 u + 83 = 53 u + 53
53 u - 50 u = 83 - 53
3 u = 30
1 u = 30 ÷ 3 = 10
Number of books in the end
= 1 u + 1
= 10 + 1
= 11
Answer(s): 11