Answer:
given below
Step-by-step explanation:
Given that an independent random sample is selected from an approximately normal population with unknown standard deviation.
To find the degrees of freedom and the critical t-value for the given sample size and confidence level
degrees of freedom=n-1
Critical t can be got from the t table in internet
a) degree of freedom =5
Critical 90% is 1.833
b) degree of freedom =20
Critical 98% is 2.528
c) degree of freedom =28
Critical 90% is 1.645
d) degree of freedom =10
Critical 99% is 3.169