The average cost of some books is $50.
If 9 of the books are now each $14 more and
3 of the books are now each $4 less,
the average cost of the books becomes $56.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
50 |
56 |
Total value |
50 u |
56 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 50 x 1 u
= 50 u
Increase in the cost after 9 books are now each $14 more and 3 books are now each $4 less
= 9 x 14 - 3 x 4
= 126 - 12
= $114
Total cost of books after 9 books are now each $14 more and 3 books are now each $4 less
= 50 u + 114
Total cost of books in the end
= 56 x 1 u
= 56 u
56 u = 50 u + 114
56 u - 50 u = 114
6 u = 114
1 u = 114 ÷ 6 = 19
Number of books in the end
= 1 u
= 19
Answer(s): 19