Question

The average local cell phone call length was reported to be 2.27 minutes. A random sample of 20 phone calls showed an average of 2.98 minutes in length with a standard deviation of 0.98 minute. At α = 0.05 can it be concluded that the average differs from the population average?

Step 1: State hypotheses by filling in the symbol (=, <, >, or not equal) and the population mean:

H_o:  μ  

H₁: μ  

Step 2: Find the critical value (from the table) (example: 2.345 or -2.345 or +/- 2.345)

Critical t value is:

Step 3: Compute the test value using the formula (round to two decimal places, example 6.45):

T test value is:

Step 4: Reject the null or do not reject the null (type in either Reject the null or do not reject the null only):

Step 5: Conclusion sentence (type in either is or is not only, to reflect what you found):

There  enough evidence to support the claim that the mean local cell phone call length differs from 2.27 minutes.

Answer 1