The average cost of 9 books is $90.
After 3 new books are added,
the average cost of all the books is $80.
- What is the total cost of the 3 books that are added?
- What is the average cost of the 3 books that are added?
(a)
Total cost of 9 books
= 9 x 90
= $810
Number of books
= 9 + 3
= 12
Total cost of all the books
= 12 x 80
= $960
Total cost of the 3 books that are added
= 960 - 810
= $150
(b)
Average cost of the 3 books that are added
= 150 ÷ 3
= $50
Answer(s): (a) $150; (b) $50