The average cost of 4 books is $90.
After 4 new books are added,
the average cost of all the books is $80.
- 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 4 books
= 4 x 90
= $360
Number of books
= 4 + 4
= 8
Total cost of all the books
= 8 x 80
= $640
Total cost of the 4 books that are added
= 640 - 360
= $280
(b)
Average cost of the 4 books that are added
= 280 ÷ 4
= $70
Answer(s): (a) $280; (b) $70