Statistic assistance needed!!!

• Apr 22nd 2008, 11:14 AM
Seansgirl1
Statistic assistance needed!!!
.A study of the amount of time it takes a mechanic to rebuild the transmission for a 1998 Acura Integra shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 mechanics are randomly selected, find the probability that their mean rebuild time exceeds 8.1 hours. u=8.4 o=1.8/√40
Z= -u Z= 8.1 -8.4 = -0.3 = -1.05 P=0.1469 found by .5000-0.3531
o√n 1.8/√40 0.285

Is this correct
• Apr 22nd 2008, 06:43 PM
mr fantastic
Quote:

Originally Posted by Seansgirl1
.A study of the amount of time it takes a mechanic to rebuild the transmission for a 1998 Acura Integra shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 mechanics are randomly selected, find the probability that their mean rebuild time exceeds 8.1 hours. u=8.4 o=1.8/√40
Z= -u Z= 8.1 -8.4 = -0.3 = -1.05 P=0.1469 found by .5000-0.3531
o√n 1.8/√40 0.285

Is this correct

No. How can Pr( X > 8.1) possibly be less than 0.5 when 8.1 < 8.4 = mean??

The answer, correct to four decimal places, is 0.8541.