The average cost of some books is $28.
After 5 new books are added,
it adds another $14 to the total cost.
As a result, the average cost of all the books decreases to $22.
How many books are there at first?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 5 |
Value |
28 |
22 |
Total value |
28 u |
22 u + 110 |
Number of books at first = 1 u
Number of books in the end = 1 u + 5
Total cost of books at first
= 28 x 1 u
= 28 u
Total cost of books in the end
= 22 x (1 u + 5)
= 22 u + 110
28 u + 14 = 22 u + 110
28 u - 22 u = 110 - 14
6 u = 96
1 u = 96 ÷ 6 = 16
Number of books at first = 16
Answer(s): 16