Question

PART I

Fill in the blank. Speed Car Rental company found that the tire lifetime for their vehicles has a mean of 47,014.81 miles and standard deviation of 5,115.88 miles. In a sample of 75 tires tested, there is a 59% chance that the average tire lifetime is less than ________ miles.

1)

46,880.39

2)

45,850.72

3)

47,149.23

4)

48,178.9

5)	There is not enough information to determine this.

PART II

An airline records flight delays in and out of Chicago O'Hare airport for a year. The average delay for these flights is 9.64 minutes with a standard deviation of 3.51 minutes. For a sample of 49 flights, 94% of flights will have an average delay less than how many minutes?

1)

4.18

2)

10.42

3)	There is not enough information to determine this.

4)

15.1

5)

8.86

Answer 1

Answer :

Part 1)

Given data is :

Sample size n = 75

Mean =   = 47,014.81

Standard deviation = = 5,115.88

Confidence interval = 59%

Z value at 59% = 0.228

Now,

Standard error = SE =

=

SE = 590.75

therefore,

= 47,014.51 + 0.228(590.75)

= 47,014.51 + 134.69

= 47,149.2

Option 3 is correct

Part 2)

Given data is :

Sample size n = 49

Average delay time = Mean = = 9.64

Standard deviation = = 3.51

Confidence interval = 94%

Z value at 94% = 1.56

therefore,

Standard error = SE =

=

SE = 0.5014

Finally corresponding value in time = Mean + Z(SE)

= 9.64 + 1.56(0.5014)

= 9.64 + 0.7823

= 10.42

Option 2 is correct