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