The average cost of some books is $30.
If 8 of the books are now each $14 more and
2 of the books are now each $6 less,
the average cost of the books becomes $35.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
30 |
35 |
Total value |
30 u |
35 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 30 x 1 u
= 30 u
Increase in the cost after 8 books are now each $14 more and 2 books are now each $6 less
= 8 x 14 - 2 x 6
= 112 - 12
= $100
Total cost of books after 8 books are now each $14 more and 2 books are now each $6 less
= 30 u + 100
Total cost of books in the end
= 35 x 1 u
= 35 u
35 u = 30 u + 100
35 u - 30 u = 100
5 u = 100
1 u = 100 ÷ 5 = 20
Number of books in the end
= 1 u
= 20
Answer(s): 20