The average cost of some books is $35.
If 5 of the books are now each $15 more and
3 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 5 books are now each $15 more and 3 books are now each $7 less
= 5 x 15 - 3 x 7
= 75 - 21
= $54
Total cost of books after 5 books are now each $15 more and 3 books are now each $7 less
= 35 u + 54
Total cost of books in the end
= 37 x 1 u
= 37 u
37 u = 35 u + 54
37 u - 35 u = 54
2 u = 54
1 u = 54 ÷ 2 = 27
Number of books in the end
= 1 u
= 27
Answer(s): 27