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August 27th, 2017, 06:00 AM  #1 
Newbie Joined: Nov 2016 From: USA Posts: 26 Thanks: 1  TI84 calculator VS. hand calculation: why different answers to same problem?
If you have a TI84 model calculator, then maybe you can figure out or explain what is causing the difference in answer when solving it by hand VS. calculator. I am finding the standard deviation of five numbers: 20, 22, 24, 26, 28 The mean of these five numbers is (120/5) = 24 Using the formula by hand, I get: SQRT [(2024)^2+(2224)^2+(2424)^2+(2624)^2+(2824)^2)/5] SQRT [(16+4+0+4+16)/5] =SQRT [40/5] =SQRT 8 =2.83 However, using the TI84 PLUS calculator I get the answer of 3.16. Here is what I found online on how to calculate standard deviation on the TI84 PLUS: 2ND LIST Tab across to select MATH #7 STD DEV StdDev({20,22,24,26,28}) ENTER Answer = 3.16 I think what the TI84 is doing is subtracting 1 from the denominator, using 4 instead of 5. SQRT (40/4) =SQRT(10) =3.16 What is going on with my calculation on the TI84 calculator? Last edited by Seventy7; August 27th, 2017 at 06:07 AM. 
August 27th, 2017, 07:32 AM  #2 
Math Team Joined: Jul 2011 From: Texas Posts: 2,628 Thanks: 1308 
The TI84 is calculating the sample standard deviation. see explanation at this link ... math.stackexchange.com/questions/15098/samplestandarddeviationvspopulationstandarddeviation 

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