Question

Select ALL the correct answers.
Marley owns a music store. The first week a new album was released, he sold 800 copies at his store. Each week after the release, the number of copies sold decreased by 11%.

Select all the functions that can be used to find the number of copies sold, f(n), n weeks after the release.

Answer 1

first week sold 800 copies
∴ at n=1  ⇒⇒⇒ f(1) = 800

Each week the number of copies sold decreased by 11%.
∴ at n = 2 ⇒⇒⇒ f(2) = 800 * (1-.11) = 800 * 0.89 = f(1) * 0.89
   at n = 3 ⇒⇒⇒ f(3) = 800 * 0.89 *0.89 = 800 * 0.89² = f(1) * 0.89 * f(2)
   at n = 4 ⇒⇒⇒ f(4) = 800 * 0.89³ = f(1) * 0.89 * f(3)
and so on .......

∴ $f(n) = 800 * 0.89^{n-1}$
    Or which can be written as
    f(1) = 800 , f(n) = 0.89 * f(n-1)  n ≥ 2

The correct choices are:
$f(n) = 800 * 0.89^{n-1}$
f(1) = 800 , f(n) = 0.89 * f(n-1)  n ≥ 2