Question

Smith Products wants its online service agents to respond to posted customer complaints in an average of 28 minutes. You track a random sample of 12 complaints. The average response time for the sample is 30.2 minutes. The sample standard deviation is 14.3 minutes. Is this sample result sufficient to reject a null hypothesis that the average response time for all customer complaints is exactly 28 minutes? Use a 5% significance level. Assume the population distribution is approximately normal.

tstat = .53. Since tstat is between -2.201 and + 2.201, we can’t reject the null hypothesis null hypothesis.

tstat = 2.73. Since tstat is outside the interval -2.332 to + 2.332, we can reject the null hypothesis null hypothesis.

tstat = 2.73. Since tstat is outside the interval -2.201 to + 2.201, we can reject the null hypothesis null hypothesis.

tstat = 1.33. Since tstat is between -2.201 and + 2.201, we can’t reject the null hypothesis null hypothesis.

Answer 1

H0: Null Hypothesis: = 28   ( The average response time for all customer complaints is exactly 28 minutes ) (Claim)

HA: Alternative Hypothesis: 26

Test Statistic is given by:

= 0.05

ndf = n - 1 = 12 - 1 = 11

From Table, critical values of t = 2.201

So,

Correct option:

tstat = .53. Since tstat is between -2.201 and + 2.201, we can’t reject the null hypothesis.