SOLUTION: Trying to get my head around normal distribution, please help. The time spent by students working on a project is a normal random variable with parameters m = 12 hours and s = 4

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Question 316275: Trying to get my head around normal distribution, please help.
The time spent by students working on a project is a normal random variable with parameters m = 12 hours and s = 4 hours. Compute the probability that
(a) the amount of time spent on the project is less than 14 hours.
(b) the amount of time spent on the project is greater than 8 hours.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
a) Find the z-score.
z=%28x-mu%29%2Fsigma=%2814-12%29%2F4=0.5
Find P%280.5%29.
P%280.5%29=0.691462
.
.
.
b) Find the z-score.
z=%28x-mu%29%2Fsigma=%288-12%29%2F4=0.5
Find P%28-1%29.
P%28-1%29=0.158655
This is the probability that covers 8 hrs and less.
You're looking for more than 8.
P(x <= 8)+P(x > 8)=1
P(x > 8)=1-P(x <= 8)
P(x > 8)=1-0.159655
P(x > 8)=0.841345