The average cost of some books is $35.
If 7 of the books are now each $14 more and
2 of the books are now each $4 less,
the average cost of the books becomes $41.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
35 |
41 |
Total value |
35 u |
41 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 35 x 1 u
= 35 u
Increase in the cost after 7 books are now each $14 more and 2 books are now each $4 less
= 7 x 14 - 2 x 4
= 98 - 8
= $90
Total cost of books after 7 books are now each $14 more and 2 books are now each $4 less
= 35 u + 90
Total cost of books in the end
= 41 x 1 u
= 41 u
41 u = 35 u + 90
41 u - 35 u = 90
6 u = 90
1 u = 90 ÷ 6 = 15
Number of books in the end
= 1 u
= 15
Answer(s): 15