Your grandma bought a piano 10years ago for $6000.it has depreciated 9% every year since .how much is it worth today

Question

Find the function 

Answer 1

w represents its worth today

 

w = 6000(0.91)¹⁰

 

Can you calculate?

Answer 2

Original Price: X = $6000
Every year it depreciates 9% means, 100% - 9% = 91% of the value remains every year! That is, the next year we would have, $6000 x 0.91 = $5460. Two years from now: $5460 x 0.91 = $4968.60, etc. 
In "t" years the formula is:

X(t) = 6000*(0.91)^t

Using t = 10, you would end up having Mark's formula above. That is, 

X(10) = 6000*(0.91)¹⁰ = $2336.50