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Nationally, the average class size in K-12 classrooms is 26 students with a standard deviation of...

Nationally, the average class size in K-12 classrooms is 26 students with a standard deviation of 3.5.  What proportion of classrooms has between 20 and 25 students?

Math   Statistics-And-Probability   
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Answer #1

The following information has been provided:

μ = 26, σ = 3.5

We need to compute Pr(20≤X≤25). The corresponding z-values needed to be computed are:

Therefore, we get:

Pr(20≤X≤25) = 0.3875 - 0.0432

Pr(20≤X≤25) = 0.3443

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