The average cost of some books is $50.
If 9 of the books are now each $12 more and
3 of the books are now each $4 less,
the average cost of the books becomes $53.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
50 |
53 |
Total value |
50 u |
53 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 $12 more and 3 books are now each $4 less
= 9 x 12 - 3 x 4
= 108 - 12
= $96
Total cost of books after 9 books are now each $12 more and 3 books are now each $4 less
= 50 u + 96
Total cost of books in the end
= 53 x 1 u
= 53 u
53 u = 50 u + 96
53 u - 50 u = 96
3 u = 96
1 u = 96 ÷ 3 = 32
Number of books in the end
= 1 u
= 32
Answer(s): 32