Question

A process manufactures ball bearings with diameters that are normally distributed with mean 25.1 millimeters and standard deviation 0.08 millimeter. (a) [5pts] What proportions of the diameters are greater than 25.4

Answer 1

The proportions of the diameters that are greater than 25.4 millimeters is 5%.

Explanation:

Given;

mean of the normal distribution, m = 25.1 millimeters

standard deviation, d = 0.08 millimeter

1 standard deviation above the mean = m + d = 25.1 + 0.08 = 25.18

2 standard deviation above mean = m + 2d = 25.1 + 2(0.08) = 25.26

3 standard deviation above the mean = m + 3d = 25.1 + 3(0.08) = 25.34

4 standard deviation above the mean = m + 4d = 25.1 + 4(0.08) = 25.42

To obtain a diameter greater than 25.4, we select data after 4 standard deviation above the mean.

Data within 4 standard deviation above the mean is 95%

Data outside 4 standard deviation above the mean is 5%

Therefore, the proportions of the diameters that are greater than 25.4 millimeters is 5%.