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Exercise 3 Solution
In this question we need to determine the value of n (sample size). But this should be, so that only 10% of the sample mean exceeds μ = 70 by 2 or more. That is X – μ = 2. From the normal distribution tables the value of z (which divides the area into the lower 90% and the upper 10%) is 1.28. By substituting this value of z =1.28 in the formula below will yield the value of n.
Z = X-μ σ /√n
1.28=72-70 10/√n
Therefore, 1.28x10/√n= 2
1.28 x10 = √n 2 6.40= √n
Thus, n= 6.40²
= 40.96 |