P235 The thickness of glass sheets produced by a certain pro

P.235

The thickness of glass sheets produced by a certain process are normally distributed with a mean of ? = 2.50 millimeters and a standard deviation of ? = 0.12 millimeters.

What is the value of c for which there is a 99% probability that a glass sheet has a thickness within the interval [ 2.50 –c, 2.50 +c]?

(a)

..............

millimeters

Solution

X = Thickness of glass sheets is normal (2.50, 0.12)

Given that

within the interval [ 2.50 –c, 2.50 +c] probability =0.99

z value = |2.58|

Thus 2.58sigma = c

c= 0.3096