The surface finish of a piece of steel is measured by a number called the Rz. Th

Question

The surface finish of a piece of steel is measured by a number called the Rz. The lower the number, the smoother the surface of the steel. on a parts conveyor line, the hardness of 9 individual pieces was tested. The parts were randomly selected. The Rockwell Hardness is assumed to be normally distributed. The measured values obtained were: 0.90, 0.85, 0.68, 0.75, 0.53, 0.80, 0.85, 0.81, 0.92 A) Find the mean of the above values B) Find the median of the above values C) Find the standard deviation of the above values D) What is the Range of the values? E) what is the "Statistical Range" (Mean +/-3 Std Deviations)?

Explanation / Answer

We can solve this question using minitab

First enter data in minitab

Click on Stats------> Basic Statistics ----------> Display descriptive statistics ---------> Select column of values ------->

Click on statistics ----------> select which value we have to need ---------> ok

We get

MTB > Describe C1;
SUBC> Mean;
SUBC> StDeviation;
SUBC> Median;
SUBC> Range.

Descriptive Statistics: C1

Variable Mean StDev Median Range
C1 0.7878 0.1214 0.8100 0.3900

a) mean = 0.7878

b) median = 0.1214

c) standard deviance = 0.1214

d) Range = 0.3900

e) Statistical range = ( mean - 3*standard deviation , mean + 3*standard deviation)

=( 0.4236 , 1.152)

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