Originally Posted by
aikawa Hello need some help on few questions
The amount of time spent by North American adults watching tv per day is normally distributed with a mean of 6 hrs and a std of 1.5 hrs.
A. what is the probability that a random selected North American adult watches tv for more than 7 hrs?
B. What is the probability that the average time watching tv by a random sample of five adults is more than 7 hrs?
C. What is the probability that in a random sample of five adults, all watch TV for more than 7 hrs per day?
Here is what i came up with
A. Z= 7-6/1.5= .6667
P(Z>.6667)=.2486
=0.5 + .2486= .7486 Mr F says: This is clearly wrong. Since 7 is greater than the mean, how can Pr(X > 7) be greater than 0.5 ....? I get 0.2525.
B. 7-6/.67= 1.49
P(Z>1.49)= 0.5- .4319= .0681 Mr F says: Correct.
C. Cannot come up with a solution
Am i on the right track? doing the calculation correct? When Z>X is it always going to me subtracting and when Z<X addition?
Some help/advice is much appreciated