The average cost of some books is $38.
When another 8 books are added,
the total cost increases by $120.
The average cost becomes $30.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 8 |
Value |
38 |
30 |
Total value |
38 u |
30 u + 240 |
Number of books at first = 1 u
Number of books in the end = 1 u + 8
Total cost of books at first
= 1 u x 38
= 38 u
Total cost of the books in the end
= 30 x (1 u + 8)
= 30 u + 240
38 u + 120 = 30 u + 240
38 u - 30 u = 240 - 120
8 u = 120
1 u = 120 ÷ 8 = 15
Number of books in the end
= 1 u + 8
= 15 + 8
= 23
Answer(s): 23