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November 9th, 2015, 11:39 AM  #1 
Newbie Joined: Nov 2015 From: Miami Posts: 2 Thanks: 0  What formula for this exponentially decreasing set of data?
I have this set of data: 0.1  40 0.2  30 0.3  25 0.4  22.5 0.5  21.75 As you can see it decrease by half of the previous increment. How can I put that as a formula? I tried something along the lines of: 40  10*(x1)/2ˆx but it's not right. How can I correct that formula? 
November 9th, 2015, 12:55 PM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 3,044 Thanks: 1627 
0.5 should have 21.25 as its function value $y = 20+40 \cdot 2^{10x}$ 
November 9th, 2015, 12:56 PM  #3 
Senior Member Joined: Mar 2011 From: Chicago, IL Posts: 214 Thanks: 77 
$\displaystyle 4010\cdot\frac{1(\frac{1}{2})^{n1}}{1\frac{1}{2}}$ n=1,2,3,... 
November 9th, 2015, 06:03 PM  #4 
Newbie Joined: Nov 2015 From: Miami Posts: 2 Thanks: 0  
November 10th, 2015, 05:18 AM  #5 
Senior Member Joined: Mar 2011 From: Chicago, IL Posts: 214 Thanks: 77  

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data, decreasing, exponentially, formula, set 
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