The average cost of some books is $44.
When another 4 books are added,
the total cost increases by $120.
The average cost becomes $40.
How many books are there in the end?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 4 |
Value |
44 |
40 |
Total value |
44 u |
40 u + 160 |
Number of books at first = 1 u
Number of books in the end = 1 u + 4
Total cost of books at first
= 1 u x 44
= 44 u
Total cost of the books in the end
= 40 x (1 u + 4)
= 40 u + 160
44 u + 120 = 40 u + 160
44 u - 40 u = 160 - 120
4 u = 40
1 u = 40 ÷ 4 = 10
Number of books in the end
= 1 u + 4
= 10 + 4
= 14
Answer(s): 14