Question

Sports store is having a closing down sale, all stock has to be sold. each day an article remains unsold, the price is discounted by 4% of the previous days price. This discounting continues until the article is sold. The table shows the price of a mountain bike during the first 5 days of the sale:

Day 1 = 750
Day 2 = 720
Day 3 = 691.20
Day 4 = 663.55
Day 5 = 637.01

A) State the growth factor

720/750 = 0.96

B) Calculate the cost of the mountain bike on the 10th day of the sale.

T10 = 750(0.96)^10-1
= 750(0.96)^9
750(0.69253) = 519.40

C) Write an expression for the cost of the mountain bike on the nth day of the sale:

$750(0.96)^n-1

D) The mountain bike was eventually sold for $359.70. On which day of the sale was it sold?

I don't get how to solve this one.

Answer 1

For D)
look at the log portion of this post,
I believe it was your post, but I can't tell since you continue to use "anonymous" for your name.

http://www.jiskha.com/display.cgi?id=1316650359

Answer 2

The bike was sold on the 19th day

359.70=750(0.96)^n-1
divide both sides by 750
0.4796=0.96^n-1
now just guess and check for n
0.4796=0.96^20-1
0.4796=0.4604
nope
0.4796=0.96^19-1
0.4796=4796
yep it works

n=19
so the bike was sold on the 19th day of the sale.
:)