Question

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?

Answer 1

`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`

Answer 2

`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`