The average cost of some books is $70.
When a book that costs $94 is added,
the average cost of the books becomes $74.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 1 |
Value |
70 |
74 |
Total value |
70 u |
74 u + 74 |
Number of books at first = 1 u
Number of books in the end = 1 u + 1
Total cost of the books at first
= 70 x 1 u
= 70 u
Total cost of books in the end
= 70 u + 94
Total cost of books in the end
= 74 x (1 u + 1)
= 74 u + 74
70 u + 94 = 74 u + 74
74 u - 70 u = 94 - 74
4 u = 20
1 u = 20 ÷ 4 = 5
Number of books in the end
= 1 u + 1
= 5 + 1
= 6
Answer(s): 6