SOLUTION: if you start out with 100 dollars on january and every month there is a 25% deduction of price, on what month will it take you to get a price under 25 dollars, and give an equation

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Question 575118: if you start out with 100 dollars on january and every month there is a 25% deduction of price, on what month will it take you to get a price under 25 dollars, and give an equation of how to find your answer.[remember each month will have a different amount.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
if you start out with 100 dollars on January and every month there is a 25% deduction of price, on what month will it take you to get a price under 25 dollars, and give an equation of how to find your answer
:
let m = month for this to be true
:
100%281-.25%29%5Em = 25
100%28.75%5Em%29 = 25
divide both side by 100
.75%5Em = 25%2F100
.75%5Em = .25
use logs here
m*log(.75) = log(.25)
m = log%28.25%29%2Flog%28.75%29
m = 4.82 ~ 5 months; it will less than $25 in May
;
:
Check on a calc enter: 100 * .75^5 results: $23.73