kancheongmum:Hi, thanks for the prompt replyHi x6michelle9xx6michelle9x:Hi, I would appreciate if someone can help to solve this problem without using algebra, thanks in advance!
The average cost of a few books was $8. After a book which costs $32 was added, the average cost becomes $12. How many books are there now?
$32 - $12 = $20 (we have to minus out the book that was added)
$20 is the amount that contribute to the increased of the average cost of a few books
$12 - $8 = $4
$20/$4 = 5 books
No. of books now --- 5+1 = 6 books (answer)
Check:
$8 x 5 = $40
$40+$32 = $72
$72/6 = $12
However, I can't figure out the rationale behind '$32 - $12 = $20'. Why does $32-$12 equals to 'minus out the book that was added'. Could you help me with this? Thanks a lot!