The average cost of some books is $20.
When a book that costs $76 is added,
the average cost of the books becomes $24.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
20 |
24 |
Total value |
20 u |
24 u + 24 |
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 + 76
Total cost of books in the end
= 24 x (1 u + 1)
= 24 u + 24
20 u + 76 = 24 u + 24
24 u - 20 u = 76 - 24
4 u = 52
1 u = 52 ÷ 4 = 13
Number of books in the end
= 1 u + 1
= 13 + 1
= 14
Answer(s): 14