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  • 1 Post By skeeter
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August 27th, 2017, 06:00 AM   #1
Joined: Nov 2016
From: USA

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TI-84 calculator VS. hand calculation: why different answers to same problem?

If you have a TI-84 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 [(20-24)^2+(22-24)^2+(24-24)^2+(26-24)^2+(28-24)^2)/5]
SQRT [(16+4+0+4+16)/5]
=SQRT [40/5]

However, using the TI-84 PLUS calculator I get the answer of 3.16.

Here is what I found online on how to calculate standard deviation on the TI-84 PLUS:

Tab across to select MATH

StdDev({20,22,24,26,28}) ENTER
Answer = 3.16

I think what the TI-84 is doing is subtracting 1 from the denominator, using 4 instead of 5.
SQRT (40/4)

What is going on with my calculation on the TI-84 calculator?

Last edited by Seventy7; August 27th, 2017 at 06:07 AM.
Seventy7 is offline  
August 27th, 2017, 07:32 AM   #2
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Joined: Jul 2011
From: Texas

Posts: 2,628
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The TI84 is calculating the sample standard deviation.

see explanation at this link ...
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