The average cost of some books is $45.
If 3 of the books are now each $12 more,
the average cost of the books becomes $48.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
45 |
48 |
Total value |
45 u |
48 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 45 x 1 u
= 45 u
Total cost of books in the end
= 48 x 1 u
= 48 u
Increase in the cost when 3 books are now each $12 more
= 3 x 12
= $36
Total cost of books after 3 books are now each $12 more
= 45 u + 36
48 u = 45 u + 36
48 u - 45 u = 36
3 u = 36
1 u = 36 ÷ 3 = 12
Number of books in the end
= 1 u
= 12
Answer(s): 12