The average cost of some books is $60.
When a book that costs $92 is added,
the average cost of the books becomes $62.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
60 |
62 |
Total value |
60 u |
62 u + 62 |
Number of books at first = 1 u
Number of books in the end = 1 u + 1
Total cost of the books at first
= 60 x 1 u
= 60 u
Total cost of books in the end
= 60 u + 92
Total cost of books in the end
= 62 x (1 u + 1)
= 62 u + 62
60 u + 92 = 62 u + 62
62 u - 60 u = 92 - 62
2 u = 30
1 u = 30 ÷ 2 = 15
Number of books in the end
= 1 u + 1
= 15 + 1
= 16
Answer(s): 16