The average cost of 9 books is $70.
After 4 new books are added,
the average cost of all the books is $50.
- 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 70
= $630
Number of books
= 9 + 4
= 13
Total cost of all the books
= 13 x 50
= $650
Total cost of the 4 books that are added
= 650 - 630
= $20
(b)
Average cost of the 4 books that are added
= 20 ÷ 4
= $5
Answer(s): (a) $20; (b) $5