In a study, the mean number of days that

130

adolescents in substance abuse treatment used medical marijuana in the last

6

months was

115.26.

Assuming the population standard deviation is

33

days, a

99%

confidence interval for the mean number of days,

,

of medical marijuana use in the last

6

months of all adolescents in substance abuse treatment is from

107.80

to

122.72,

and a

90%

confidence interval for the mean is from

110.50

to

120.02.

Complete parts (a) through (c) below.

Click here to view page 1 of the table of areas under the standard normal curve.

LOADING...

Click here to view page 2 of the table of areas under the standard normal curve.

LOADING...

a. Determine the margin of error for the

99%

confidence interval.

enter your response here

day(s)

(Round to two decimal places as needed.)

b. Determine the margin of error for the

90%

confidence interval.

enter your response here

day(s)

(Round to two decimal places as needed.)

c. Compare the margins of error found in parts (a) and (b). What principle is being illustrated?

The margin of error found in part (b) is

greater than

within 0.05 of

less than

the margin of error found in part (a). The principle being illustrated here is that increasing the

confidence level

sample mean

sample size

population standard deviation

increases

does not change

decreases

the margin of error of a confidence interval

for a fixed confidence level.

for a fixed sample size.

regardless of changes to any other values used in computing the interval.