The average cost of some books is $48.
If 3 of the books are now each $15 more,
the average cost of the books becomes $51.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
48 |
51 |
Total value |
48 u |
51 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 48 x 1 u
= 48 u
Total cost of books in the end
= 51 x 1 u
= 51 u
Increase in the cost when 3 books are now each $15 more
= 3 x 15
= $45
Total cost of books after 3 books are now each $15 more
= 48 u + 45
51 u = 48 u + 45
51 u - 48 u = 45
3 u = 45
1 u = 45 ÷ 3 = 15
Number of books in the end
= 1 u
= 15
Answer(s): 15