Question

A random sample of 20 seniors from a large school district had a
mean Math SAT score of 450 and a sample standard deviation of 85.
Suppose we wanted to plan a similar study with just female seniors.
We want to have a margin of error of 25 with 95% confidence. What
is the sample size needed to achieve this margin of error? Assume
that the standard deviation *s* = 100.

Answer #2

Solution :

Given that,

Population standard deviation = = 100

Margin of error = E = 25

At 95% confidence level the z is,

= 1 - 95%

= 1 - 0.95 = 0.05

/2 = 0.025

Z/2 = Z0.025 = 1.96

sample size = n = [Z/2* / E] 2

n = [1.96 *100 / 25]2

n = 61.46

Sample size = n = 62

answered by: anonymous

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