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 minimum score that b

Question 1202137: 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 minimum score that belongs to the upper 15% of the group?
Answer by ikleyn(52791) (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 minimum score that belongs
to the upper 15% of the group?
~~~~~~~~~~~~~~~

This score is the raw mark such that the area under the given normal curve on the left of this mark 
is 100% - 15% = 85% 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(0.85,  75, 15).


ANSWER.   = 90.55.   You may round it, if it is needed.

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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