SOLUTION: a random sample of size 35 is drawn from a normal distribution with mean 30 and variance 25. what is the probability that the sample mean is at least 28?

Question 1147103: a random sample of size 35 is drawn from a normal distribution with mean 30 and variance 25. what is the probability that the sample mean is at least 28?
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
Use the Normal Distribution and table of z-values
:
standard deviation = square root(25) = 5
:
standard error = 5/square root(35) = 0.8452
:
z = (28 - 30)/0.8452 is approximately -2.37
:
The probability(P) associated with the z value is 0.0089
:
P(X > or = 28) = 1 - 0.0089 = is approximately 0.9911
:

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