The average cost of 9 books is $80.
After 4 new books are added,
the average cost of all the books is $60.
- What is the total cost of the 4 books that are added?
- What is the average cost of the 4 books that are added?
(a)
Total cost of 9 books
= 9 x 80
= $720
Number of books
= 9 + 4
= 13
Total cost of all the books
= 13 x 60
= $780
Total cost of the 4 books that are added
= 780 - 720
= $60
(b)
Average cost of the 4 books that are added
= 60 ÷ 4
= $15
Answer(s): (a) $60; (b) $15