Suppose you select 25 Douglas College students at random and determine their ages. Using those 25 numbers, you calculate the sample mean, ?̅ = 21.5 years, and sample standard deviation, ? = 3.1 years...

 Suppose you select 25 Douglas College students at random and determine
their ages.

Using those 25 numbers, you calculate the sample mean, ?̅ = 21.5 years, and sample
standard deviation, ? = 3.1 years

The confidence interval for ?, the population mean age of Douglas College students, at
confidence level 1 − ?, is:
(?̅ − ??/2 ⋅
?/
√?
,?̅ + ??/2 ⋅
?/
√?
)

a. Determine the critical ? value for a 99% confidence level.

b. Find the 99% confidence interval for ?.