# Confidence Interval and null hypothesis

The null hypothesis is V = 72.4 and alternative hypothesis is V does not equal 72.4. The sample mean is 68.325 and sample standard deviation is 14.172 from a sample of size 45. Find the 95% confidence interval.

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95% confidence interval:

1. Calculate the estimated standard error of the mean ('SEM'):

SEM = standard deviation / square root ('SQRT') of sample size

= 14.172 / SQRT(45) = 2.11

2. Calculate df:

df = n-1 = 45-1 = 44

3. Determine t value for 95% confidence:

Use Student's t distribution table to ...