The average cost of some books is $50.
When a book that costs $86 is added,
the average cost of the books becomes $54.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
50 |
54 |
Total value |
50 u |
54 u + 54 |
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 + 86
Total cost of books in the end
= 54 x (1 u + 1)
= 54 u + 54
50 u + 86 = 54 u + 54
54 u - 50 u = 86 - 54
4 u = 32
1 u = 32 ÷ 4 = 8
Number of books in the end
= 1 u + 1
= 8 + 1
= 9
Answer(s): 9