The average cost of some books is $34.
If 2 of the books are now each $12 more,
the average cost of the books becomes $36.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
34 |
36 |
Total value |
34 u |
36 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
= 36 x 1 u
= 36 u
Increase in the cost when 2 books are now each $12 more
= 2 x 12
= $24
Total cost of books after 2 books are now each $12 more
= 34 u + 24
36 u = 34 u + 24
36 u - 34 u = 24
2 u = 24
1 u = 24 ÷ 2 = 12
Number of books in the end
= 1 u
= 12
Answer(s): 12