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