Question

Question 3 cont. - part 2 marks

b) An engineer studying whether a downhill section of a highway needs to be widened, measures the speed of motorists travelling along the highway. A sample of 90 cars gives a mean speed of 110.2 km/h and a standard deviation of 6 km/h.

Minitab Output 3.1 and 3.2 was obtained

Minitab Output 3.1: 
One-Sample T
Test of mu = 112 vs not= 112 

N   Mean     StDev   SE Mean   95% CI               T      P  
90  110.200  6.000   0.632     (108.943, 111 .457)  -2.85  0.005


Minitab Output 3.2:
One-Sample T
Test of mu = 112 vs < 112
95% Upper 

N   Mean     StDev  SE Mean   Bound                 T      P 
90  110.200  6.000  0.632     111.251               -2.85  0.003

(i) Find the 95% Confidence Interval for the mean speed.

Answer 1