The average cost of some books is $24.
After 6 new books are added,
it adds another $14 to the total cost.
As a result, the average cost of all the books decreases to $19.
How many books are there at first?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u + 6 |
Value |
24 |
19 |
Total value |
24 u |
19 u + 114 |
Number of books at first = 1 u
Number of books in the end = 1 u + 6
Total cost of books at first
= 24 x 1 u
= 24 u
Total cost of books in the end
= 19 x (1 u + 6)
= 19 u + 114
24 u + 14 = 19 u + 114
24 u - 19 u = 114 - 14
5 u = 100
1 u = 100 ÷ 5 = 20
Number of books at first = 20
Answer(s): 20