no exel please also theres D) (lower limit, upper limit) 7. The makers of a soft

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no exel please also theres D) (lower limit, upper limit)

7. The makers of a soft drink want to identify the average age of its consumers. A sample of 225 consumers is taken. The average age in the sample was 22 years with a population standard deviation of 6 years. Assume the population of consumer ages is normally distributed. Constru an 90% confidence interval for the average age of all the consumers (accurate to two decimal places). (20 pts.) a. Draw Distribution. b. Draw lower and Upper Limit. c. Write Formula and Substitute Values. Look up Z-value.

Explanation / Answer

Ans:

Given that

sample size,n=225

sample mean=22

population standard deviation=6

sampling distribution of sample means:

mean=22

standard error of mean=6/sqrt(225)=0.4

z value for 90% confidence interval is +/-1.645

(as alpha=1-0.9=0.1,z=normsinv(0.05)=-1.645 and z=normsinv(0.95)=1.645)

90% confidence interval for population mean

=22+/-1.645*0.4

=22+/-0.66

=(21.34, 22.66)

lower limit=21.34

upper limit=22.66

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