The average cost of some books is $20.
When a book that costs $92 is added,
the average cost of the books becomes $23.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
20 |
23 |
Total value |
20 u |
23 u + 23 |
Number of books at first = 1 u
Number of books in the end = 1 u + 1
Total cost of the books at first
= 20 x 1 u
= 20 u
Total cost of books in the end
= 20 u + 92
Total cost of books in the end
= 23 x (1 u + 1)
= 23 u + 23
20 u + 92 = 23 u + 23
23 u - 20 u = 92 - 23
3 u = 69
1 u = 69 ÷ 3 = 23
Number of books in the end
= 1 u + 1
= 23 + 1
= 24
Answer(s): 24