The average cost of some books is $41.
If 2 of the books are now each $10 more,
the average cost of the books becomes $43.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
41 |
43 |
Total value |
41 u |
43 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
= 43 x 1 u
= 43 u
Increase in the cost when 2 books are now each $10 more
= 2 x 10
= $20
Total cost of books after 2 books are now each $10 more
= 41 u + 20
43 u = 41 u + 20
43 u - 41 u = 20
2 u = 20
1 u = 20 ÷ 2 = 10
Number of books in the end
= 1 u
= 10
Answer(s): 10