In: Statistics and Probability
3. The time spent commuting from home to work for all employees of a very large company has a normal distribution with a mean of 43.4 minutes and a standard deviation of 12.1 minutes. Calculate the probability that the mean time spent commuting from home to work by a sample of 21 employees will be in between 43.26 and 49.35.
Solution :
Given that,
mean =
= 43.4
standard deviation =
= 12.1
n = 21
=
= 43.4
=
/
n = 12.1 /
21 = 2.64
P(43.26 <
< 49.35)
= P[(43.26 - 43.4) / < (
-
)
/
< (49.35 - 43.4) / )]
= P( -0.05 < Z < 2.25)
= P(Z < 2.25 ) - P(Z < -0.05)
Using z table,
= 0.9878 - 0.4801
= 0.5077