The average cost of some books is $26.
After 4 new books are added,
it adds another $14 to the total cost.
As a result, the average cost of all the books decreases to $17.
How many books are there at first?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 4 |
Value |
26 |
17 |
Total value |
26 u |
17 u + 68 |
Number of books at first = 1 u
Number of books in the end = 1 u + 4
Total cost of books at first
= 26 x 1 u
= 26 u
Total cost of books in the end
= 17 x (1 u + 4)
= 17 u + 68
26 u + 14 = 17 u + 68
26 u - 17 u = 68 - 14
9 u = 54
1 u = 54 ÷ 9 = 6
Number of books at first = 6
Answer(s): 6