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# Lowest standard deviation of measurements

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As the Quality Control Manager of a chemical company, you are asked to decide between several process methods that are supposed to uniformly mix 37.4 milligrams into a chemical solution. The resulting solutions from each process are sample tested for uniformity. The test samples yielded the following results of percentage powder mixed in the solution:

Method A: 0.13%, 0.21%, 0.009%, 0.014%
Method B: 0.10%, 0.006%, 0.015%, 0.11%, 0.16%
Method C: 0.006%, 0.09%, 0.07%
Method D: 0.18%, 0.16%, 0.19%, 0.17%

Which method would be the best choice to provide a uniform mixture??? (Hint: The best selection would be that resulting in the lowest standard deviation of measurements
Method A
Method B
Method C
Method D

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https://brainmass.com/engineering/chemical-engineering/lowest-standard-deviation-measurements-47665

#### Solution Preview

Standard Deviation:
The standard deviation is the square root of the average squared deviation from the mean.

Method A: Consider the observations: 0.13%, 0.21%, 0.009%, 0.014%
1. First, calculate the mean and determine N.
2. Remember, the mean is the sum of scores divided by N where N is the number of samples.
3. Therefore, the mean = (.13 + .21 + .009+ .014) / 4 or .09075
4. Then, calculate the standard deviation as illustrated below.
squared
sample mean ...

#### Solution Summary

The lowest standard deviation of measurements is calculated. The excel calculations are copied into a word document which is also in the solution text box.

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