The average cost of some books is $41.
If 4 of the books are now each $15 more,
the average cost of the books becomes $44.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
41 |
44 |
Total value |
41 u |
44 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 41 x 1 u
= 41 u
Total cost of books in the end
= 44 x 1 u
= 44 u
Increase in the cost when 4 books are now each $15 more
= 4 x 15
= $60
Total cost of books after 4 books are now each $15 more
= 41 u + 60
44 u = 41 u + 60
44 u - 41 u = 60
3 u = 60
1 u = 60 ÷ 3 = 20
Number of books in the end
= 1 u
= 20
Answer(s): 20