Question

A simple random sample of 40 recorded speeds (in mph) is obtained from cars traveling on a section of Highway 405 in Los Angeles. The sample has a mean of 68.4 mph and a standard deviation of 5.7 mph. Use a 0.05 level of significance to test the claim that the mean speed of all cars is greater that the posted speed limit of 65 mph

Answer 1

H0: Null Hypothesis: 65

HA: Alternative Hypothesis: > 65

SE = s/

= 5.7/ = 0.9012

Test statistisc is:

t = ( - )/SE

= (68.4 - 65)/0.9012 = 3.7727

ndf = 40 - 1 = 39

= 0.05

One tail - right side test

From Table, critical value of t = 1.6849

Since the calculated value of t = 3.7727 is greater than critical value of t = 1.6849, Reject H0.

Conclusion:
The data support the claim that the mean speed of all cars is greater than the posted speed limit of 65 mph.