The average cost of some books is $80.
When a book that costs $98 is added,
the average cost of the books becomes $83.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
80 |
83 |
Total value |
80 u |
83 u + 83 |
Number of books at first = 1 u
Number of books in the end = 1 u + 1
Total cost of the books at first
= 80 x 1 u
= 80 u
Total cost of books in the end
= 80 u + 98
Total cost of books in the end
= 83 x (1 u + 1)
= 83 u + 83
80 u + 98 = 83 u + 83
83 u - 80 u = 98 - 83
3 u = 15
1 u = 15 ÷ 3 = 5
Number of books in the end
= 1 u + 1
= 5 + 1
= 6
Answer(s): 6