Question

2.

Complete the problems below.

a. A sample 81 desktop PCs have a mean lifespan of 7.5 years and a sample standard deviation of 3.2 years. Construct a 99% confidence interval for the mean lifespan of desktop PCs.(ROUND TO 3 DECIMAL PLACES)

Confidence Interval ( ___________________Q6 , ___________________Q7)

b. When consumers apply for credit, their credit is rated using FICO scores. Credit ratings are given below for a sample of car loan applicants. Use the sample data to construct a 99% confidence interval for the mean FICO score of all applicants for credit.

(ROUND TO THE NEAREST WHOLE NUMBER) assume requirements are fulfilled.

661 595 548 730 791 678 672 491 492 583 762 624 769 729 734 706

Confidence Interval ( ___________________Q8 , ___________________Q9)

c. The IQ scores of the normal adult population has a mean of 100 IQ points and the standard deviation is 15 IQ points.

Find the sample size needed to estimate the mean IQ of professors given we want 93% confidence that the sample mean is within 4 IQ points of the population

mean.

(USE YOUR ANSWER FROM PROBLEM #1a for critical value).

n=_____________Q10

Answer 1

2)

a) The confidence interval for true mean based on the sample mean is

Here ,.

The 99% CI is

b) The given data is

X <- c(661, 595, 548, 730, 791, 678, 672, 491, 492, 583, 762, 624, 769, 729, 734 ,706)

R commands.

length(X)
mean(X)
sd(X)
The sample mean is and sample standar deviation is and sample size is .

The confidence interval for true mean based on the sample mean is

The 99% CI is

c) The margin of error is .

We need,

The required sample size is .