A store has a sale on books. The price is $17.55 for one book, $16.70 each for 2 books, $15.85 each for 3 books, and $15 each for 4 books. If this pattern continues, how much per book will it cost to buy 7 books?

2 Answers
Nov 9, 2016

Answer:

#T_7 = $12.45#

Cost for 7 books will be #$12.45# per book

Explanation:

The price per book forms an AP

#T_n: 17.55" " 16.70" "15.85" "15" "#they all differ by #-0.85#

#n:" "1" "2" "3" "4#

The cost if 7 books are bought will be #T_7#

#T_7 = a + d(n-1)#

#T_7 = 17.55-0.85xx6#

#T_7 = $12.45#

Nov 9, 2016

Answer:

#color(green)($12.45)#

Explanation:

Price difference with each additional book purchased is #$0.85#
#color(white)("XXX")(=$17.55-$16.70=$16.70-$15.85=$1585-$15.00)#

The formula for price per books seems to be:
#color(white)("XXX")p(n)=$17.55-(n-1) * $0.85#
where #n# is the number of books purchased.

#p(7)=$17.55-6 * $0.85 = $17.55 - $5.10 = $12.45#