In: Statistics and Probability
According to a 2004 report by Roger Boe et. Al. of Correctional Service Canada, the mean length of a Canadian jail sentence in 2001/2002 was ? = 4.10 months with σ = 9.75 months.
a) Can we assume that prison sentences are normally distributed? Please explain.
b) Using the central limit theorem, what is the approximate probability that the mean sentence for a random sample of 225 prisoners is more than 4.75 months?
Solution :
Given that ,
mean = 
 = 4.10
standard deviation = 
 = 9.75
n = 225
(a)
this is sampling distribution of narmal population standARD DEVIATION KNOWN
AND SAMPLE MEAN
(b)

= 4.10

= 
 / 
n = 9.75 / 
225 = 0.65
P(
 >4.75 ) = 1 - P(
< 4.75)
= 1 - P[(
- 
) / 
< (4.75-4.10) /0.65 ]
= 1 - P(z <1 )
Using z table
= 1 - 0.8413
= 0.1587
probability= 0.1587