The average cost of 6 books is $90.
After 3 new books are added,
the average cost of all the books is $70.
- 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 6 books
= 6 x 90
= $540
Number of books
= 6 + 3
= 9
Total cost of all the books
= 9 x 70
= $630
Total cost of the 3 books that are added
= 630 - 540
= $90
(b)
Average cost of the 3 books that are added
= 90 ÷ 3
= $30
Answer(s): (a) $90; (b) $30