The average cost of some books is $48.
If 2 of the books are now each $15 more,
the average cost of the books becomes $50.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
48 |
50 |
Total value |
48 u |
50 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
= 50 x 1 u
= 50 u
Increase in the cost when 2 books are now each $15 more
= 2 x 15
= $30
Total cost of books after 2 books are now each $15 more
= 48 u + 30
50 u = 48 u + 30
50 u - 48 u = 30
2 u = 30
1 u = 30 ÷ 2 = 15
Number of books in the end
= 1 u
= 15
Answer(s): 15