SOLUTION: In a National Achievement Test, the mean was found to be 75 and the standard deviation was 15. The scores also approximate the normal distribution. What is the score that divide th

Question 1202139: In a National Achievement Test, the mean was found to be 75 and the standard deviation was 15. The scores also approximate the normal distribution. What is the score that divide the distribution in two such that 75% of the cases below it?
Answer by ikleyn(52835) (Show Source): You can put this solution on YOUR website!
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In a National Achievement Test, the mean was found to be 75 and the standard deviation was 15.
The scores also approximate the normal distribution. What is the score that divide the distribution
in two such that 75% of the cases below it?
~~~~~~~~~~~~~~~~~~~~~~

This score is the raw mark such that the area under the given normal curve on the left of this mark 
is 75% of the total area. You can find it using a regular calculator TI-83 or TI-84 
with the standard function invNorm (inverse to cumulative normal distribution function)

                     area  mean SD   <<<---===  formatting pattern.
     = invNorm(0.75,  75, 15).


ANSWER.   = 85.1173.  You may round it, if you need it.

Solved.

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Alternatively, you may use an online free of charge calculator
https://onlinestatbook.com/2/calculators/inverse_normal_dist.html

If you are a beginner student, I insistently recommend you to play with this online calculator.

It has convenient, intuitively clear interface and shows the area of interest,
so you quickly will learn the subject, the meaning and the technique of these calculations and will be happy.

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