Answer: b. The 99% interval is longer.
Step-by-step explanation:
The formula to find the confidence interval for mean :
, where is the sample mean , is the population standard deviation , n is the sample size and is the two-tailed test value for z.
For 95% confidence interval the two-tailed test value for z is .
For 99% confidence interval the two-tailed test value for z is .
Since the interval is directly proportion al to the z-value , so it is clear that the width of the interval would be longer with z =3 than z=2.
i.e. The <u>99% interval</u> is longer than 95% confidence interval .