The average cost of some books is $80.
When a book that costs $94 is added,
the average cost of the books becomes $82.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
80 |
82 |
Total value |
80 u |
82 u + 82 |
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 + 94
Total cost of books in the end
= 82 x (1 u + 1)
= 82 u + 82
80 u + 94 = 82 u + 82
82 u - 80 u = 94 - 82
2 u = 12
1 u = 12 ÷ 2 = 6
Number of books in the end
= 1 u + 1
= 6 + 1
= 7
Answer(s): 7