EXAMPLE 6.5

How sample size affects the confidence interval. As in Example 6.4, the sample mean of the college savings fund contribution is $1768 and the population standard deviation is $1483. Suppose that the sample size is only 177 but still large enough for us to rely on the central limit theorem. In this case, the margin of error for 95% confidence is

and the approximate 95% confidence interval is

= (1657, 1879)