The average cost of 7 books is $60.
After 4 new books are added,
the average cost of all the books is $40.
- 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 7 books
= 7 x 60
= $420
Number of books
= 7 + 4
= 11
Total cost of all the books
= 11 x 40
= $440
Total cost of the 4 books that are added
= 440 - 420
= $20
(b)
Average cost of the 4 books that are added
= 20 ÷ 4
= $5
Answer(s): (a) $20; (b) $5