The average cost of some books is $50.
If 4 of the books are now each $10 more and
2 of the books are now each $7 less,
the average cost of the books becomes $52.
How many books are there altogether?
|
Case 1 |
Case 2 |
Number |
1 u |
1 u |
Value |
50 |
52 |
Total value |
50 u |
52 u |
Number of books at first = 1 u
Number of books in the end = 1 u
Total cost of the books at first
= 50 x 1 u
= 50 u
Increase in the cost after 4 books are now each $10 more and 2 books are now each $7 less
= 4 x 10 - 2 x 7
= 40 - 14
= $26
Total cost of books after 4 books are now each $10 more and 2 books are now each $7 less
= 50 u + 26
Total cost of books in the end
= 52 x 1 u
= 52 u
52 u = 50 u + 26
52 u - 50 u = 26
2 u = 26
1 u = 26 ÷ 2 = 13
Number of books in the end
= 1 u
= 13
Answer(s): 13