The average cost of some books is $47.
If 3 of the books are now each $10 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 |
47 |
50 |
Total value |
47 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
= 47 x 1 u
= 47 u
Total cost of books in the end
= 50 x 1 u
= 50 u
Increase in the cost when 3 books are now each $10 more
= 3 x 10
= $30
Total cost of books after 3 books are now each $10 more
= 47 u + 30
50 u = 47 u + 30
50 u - 47 u = 30
3 u = 30
1 u = 30 ÷ 3 = 10
Number of books in the end
= 1 u
= 10
Answer(s): 10