Question

withdrawal occurd when a person who uses drugs or alcohol excessivley suddenlt stops use. studies show that the onset of withdrawal is experienced a mean of 40 hours after last use with standard deviation of 18 hours. a sample of 38 people who use is to be taken what is the probability that the sample mean time between the the last use and onset withdrawal is 38 hours or less.

Answer 1

Solution:

Given that X follows a distribution with

   = 40

   = 18

A sample of size n = 38 is taken from this population.

Let be the sample mean.we know the distribution of is normal with

Mean = = = 40

SD =    = = 18 /38​ = 2.91998558 (It is called as the standard error of the mean)

Find P(sample mean time is 38 hours or less)

= P(    38)

= P[( - )/  (38 - )/ ]

= P[Z   (38 - 40)/2.91998558 ]

= P[Z -0.6849 ]

= 0.2467 ...use Z table to find P[Z -0.6849 ]