The average cost of some books is $34.
If 3 of the books are now each $11 more,
the average cost of the books becomes $37.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
34 |
37 |
Total value |
34 u |
37 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
= 37 x 1 u
= 37 u
Increase in the cost when 3 books are now each $11 more
= 3 x 11
= $33
Total cost of books after 3 books are now each $11 more
= 34 u + 33
37 u = 34 u + 33
37 u - 34 u = 33
3 u = 33
1 u = 33 ÷ 3 = 11
Number of books in the end
= 1 u
= 11
Answer(s): 11