The average cost of some books is $30.
When a book that costs $96 is added,
the average cost of the books becomes $33.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
30 |
33 |
Total value |
30 u |
33 u + 33 |
Number of books at first = 1 u
Number of books in the end = 1 u + 1
Total cost of the books at first
= 30 x 1 u
= 30 u
Total cost of books in the end
= 30 u + 96
Total cost of books in the end
= 33 x (1 u + 1)
= 33 u + 33
30 u + 96 = 33 u + 33
33 u - 30 u = 96 - 33
3 u = 63
1 u = 63 ÷ 3 = 21
Number of books in the end
= 1 u + 1
= 21 + 1
= 22
Answer(s): 22