3. You desire to do a study of juvenile drug offenders in Michigan prisons. A pr

Question

3. You desire to do a study of juvenile drug offenders in Michigan prisons. A preliminary study reveals that the mean amount of cocaine on which sentences of 20 years to life were based for a random sample of 196 juvenile drug offenders was 1.2 lbs. with a standard deviation of .2 lbs. Perform a 95% confidence interval on the mean amount of cocaine on which these sentences were based, and provide the interval. What exactly does this confidence interval tell me? (Be scientific, not sociological.) You can perform this problem by hand or by Excel, but show your work.

Explanation / Answer

n =196 , s = 0.2 , mean = 1.2
z value at 95% CI = 1.96

CI = mean +/ - z * ( s / sqrt(n))
= 1.2 +/ - 1.96 * ( 0.2/sqrt(196))
= ( 1.172, 1.228)

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