The average cost of some books is $35.
If 6 of the books are now each $11 more and
2 of the books are now each $7 less,
the average cost of the books becomes $37.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
35 |
37 |
Total value |
35 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
= 35 x 1 u
= 35 u
Increase in the cost after 6 books are now each $11 more and 2 books are now each $7 less
= 6 x 11 - 2 x 7
= 66 - 14
= $52
Total cost of books after 6 books are now each $11 more and 2 books are now each $7 less
= 35 u + 52
Total cost of books in the end
= 37 x 1 u
= 37 u
37 u = 35 u + 52
37 u - 35 u = 52
2 u = 52
1 u = 52 ÷ 2 = 26
Number of books in the end
= 1 u
= 26
Answer(s): 26