The average cost of some books is $61.
When another 6 books are added,
the total cost increases by $190.
The average cost becomes $50.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 6 |
Value |
61 |
50 |
Total value |
61 u |
50 u + 300 |
Number of books at first = 1 u
Number of books in the end = 1 u + 6
Total cost of books at first
= 1 u x 61
= 61 u
Total cost of the books in the end
= 50 x (1 u + 6)
= 50 u + 300
61 u + 190 = 50 u + 300
61 u - 50 u = 300 - 190
11 u = 110
1 u = 110 ÷ 11 = 10
Number of books in the end
= 1 u + 6
= 10 + 6
= 16
Answer(s): 16