The average cost of some books is $34.
If 4 of the books are now each $10 more,
the average cost of the books becomes $38.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
34 |
38 |
Total value |
34 u |
38 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 34 x 1 u
= 34 u
Total cost of books in the end
= 38 x 1 u
= 38 u
Increase in the cost when 4 books are now each $10 more
= 4 x 10
= $40
Total cost of books after 4 books are now each $10 more
= 34 u + 40
38 u = 34 u + 40
38 u - 34 u = 40
4 u = 40
1 u = 40 ÷ 4 = 10
Number of books in the end
= 1 u
= 10
Answer(s): 10