Richard wants to compare the data transfer rate of two internet connections. The difference between the means of samples taken for the two connections is 18 Mbps. The standard deviation of the distribution of the difference between the sample means is 6.64. Which statement is true if we are testing the null hypothesis at the 95% confidence level?
A.The difference between the two means is significant at the 95% confidence level, so the null hypothesis must be rejected.
B.The difference between the two means is significant at the 95% confidence level, so the null hypothesis must be accepted.
C.The difference between the two means is not significant at the 95% confidence level, so the null hypothesis must be rejected.
D.The difference between the two means is not significant at the 95% confidence level, so the null hypothesis must be accepted.

Given that Richard wants to compare the data transfer rate of two internet connections. The difference between the means of samples taken for the two connections is 18 Mbps. The standard deviation of the distribution of the difference between the sample means is 6.64.

Null hypothesis would be difference =0

Test statistic = 18/6.64=2.72

For 95% confidence level Z critical would be 1.96

Since 2.72 lies outside (-1.96,1.96) the conclusion would be difference is significant.

Hence null hypothesis should be rejected.

So answer is

A.The difference between the two means is significant at the 95% confidence level, so the null hypothesis must be rejected.