Question

Please use the accompanying Excel data set or accompanying Text file data set when completing the following exercise. A machine produces metal rods used in an automobile suspension system. A random sample of 15 rods is selected and the diameter is measured. The resulting data (in millimeters) are as follows: No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Dia. 8.23 8.16 8.23 8.25 8.26 8.23 8.20 8.26 8.19 8.23 8.20 8.28 8.24 8.25 8.24 Use the data above to calculate a 95% two-sided confidence interval on the mean rod diameter. Assume the data are normally distributed. (a) Calculate the sample mean and standard deviation. Round the sample mean and the sample standard deviation to 2 and 3 decimal places respectively (e.g. 98.76 and 98.765). (b) Calculate the 95% two-sided confidence interval on the true mean rod diameter. Round your answers to 3 decimal places (e.g. 98.765).

Answer 1

Answer:

(8.213 ; 8.247)

Step-by-step explanation:

Given the data :

No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Dia. 8.23 8.16 8.23 8.25 8.26 8.23 8.20 8.26 8.19 8.23 8.20 8.28 8.24 8.25 8.24

Sanple size, n = 15

Sample mean, xbar = Σx / n = 123.45 / 15 = 8.23

The sample standard deviation, s = √(x -xbar)²/n-1

Using calculator :

Sample standard deviation, s = 0.03116

s = 0.031 (3 decimal places)

The 95% confidence interval :

C.I = xbar ± (Tcritical * s/√n)

Tcritical at 95%, df = 15 - 1 = 14

Tcritical = 2.145

C.I = 8.23 ± (2.145 * 0.031/√15)

C.I = 8.23 ± 0.0171689

C.I = (8.213 ; 8.247)