SOLUTION: The life time of a certain electrical part is normal random variable with mean life 100 hours and standard deviation 20 hours. If 16 such parts are tested, find the probability tha

Algebra ->  Probability-and-statistics -> SOLUTION: The life time of a certain electrical part is normal random variable with mean life 100 hours and standard deviation 20 hours. If 16 such parts are tested, find the probability tha      Log On


   

Question 918527: The life time of a certain electrical part is normal random variable with mean life 100 hours and standard deviation 20 hours. If 16 such parts are tested, find the probability that the sample mean is
a. Less than 104:
b. Between 98 and 104 hours.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
z+=blue+%28x+-+mu%29%2Fblue%28sigma%2Fsqrt%28n%29%29
z+=blue+%28x+-+100%29%2Fblue%2820%2Fsqrt%2816%29%29
a) z = 4/5, P(x <104) = P(z < 4/5) = normalcdf(-100, .8)
b) z = -2/5 and 4/5
P(98 < x < 104) = P(-.4 < z < .8) = normalcdf(-.4, .8)