Answer: 1.302
Step-by-step explanation:
The sample used was 43 retirees, so n=43. To find the degrees of freedom:
df=n−1=43−1=42
The confidence level is given in the scenario: 80%. So,
α=1−CL=1−0.8=0.2
But we want to use the value for α2, which is 0.22=0.1. Using the table, we need to find the row for 42 degrees of freedom, and the column for t0.1. So, the t-score we would use to find the 80% confidence interval is 1.302.
We could also use a calculator and input 1−α2=0.9 and the degrees of freedom into invT, in which case we would enter invT(0.9,42).
