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Inaccurate Area under normal curve

Department of Math and CS GeoGebra Templates for WeBWorK shared this question 5 years ago

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I am using geogebra to provide interactive graph of the standard normal distribution for a WeBWorK question.

The area under the curve is not being calculated with as much accuracy as I need.

P(Z<-1.91) is 0.0281 but setting the sliding point to -1.91 on the graph shows an area of 0.0274.

You can find the graph in question at https://www.geogebra.org/m/a9z9GKKB.

I have used Normal(meanPop, stdDevPop, x) to graph the function with meanPop=0 and stdDevPop=1.

Any ideas?

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Best Answer

mathmagic ● 5 years ago

hello

xminVal lost accuracy in shadedAreaLeft

change xminVal by -100, i.e.

saludos

Comments (6)

ccambre ● 5 years ago

use the probability calculator for this question. You can find the tool in the toolbar of the Spreadsheet.

It gives the correct result

chris

e93bfe155ee93be4c4775820e335e8b4

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Department of Math and CS GeoGebra Templates for WeBWorK ● 5 years ago

Unfortunately, the probability calculator does not export to WeBWorK, though this would be my preference.

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mathmagic ● 5 years ago ●

hello

xminVal lost accuracy in shadedAreaLeft

change xminVal by -100, i.e.

saludos

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Department of Math and CS GeoGebra Templates for WeBWorK ● 5 years ago

Yep. I tried to do with fewer variables by using the xMinVal and xMaxVal that can be reset in WeBWorK for the area limits as well. This is exactly the problem. Though now that I think about it I can hard code the outside tail limits to -100 and +100 since they'll never need to be altered.

Thank you kindly, I am sure this will take care of it.

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Michael Borcherds ● 5 years ago

If you want it even more accurate, you can define the pdf and use that:

F(x) = -1 / 2 erf(-x sqrt(2) / 2 )

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ccambre ● 5 years ago

"the probability calculator does not export to WeBWorK"

you can show the probability calculator in the main window by clicking on the icon in the upperright corner of the prob.calc. Then it behaves as any GG file with the same possibilities of exportation.

chris

a86eaee4da16481dc2271db9c64d65b6

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