Question

The parent population mean grade, μ, on a final exam was 81, and the parent population standard deviation, σ, was 10. The instructor grades such that only the top 10% of the class receives an A on the final exam, assuming the grades follow a normal distribution (assumed because the number of students is seemingly infinite). What is the minimum grade necessary to make an A on the final?

the answer is found using x=mue+tau(sigma)

we know everything except tau. Explain in great detail please all that is included in finding tau.

Answer 1

The following information has been provided:

We need to compute

The corresponding z-value needed to be computed is:

We get that

Here 1.281551566 is the P(Z>z) = 0.10 of the standard normal distribution

Hence the minimum grade is 93.8 ~ 94

The following is obtained graphically:

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