SOLUTION: Given the following frequency distribution, find the mean, variance, and standard deviation. Please show all of your work. Errors Frequency 36-38 18 39-41 7 42-44 12 45-47 22

Question 507513: Given the following frequency distribution, find the mean, variance, and standard deviation. Please show all of your work.
Errors Frequency
36-38 18
39-41 7
42-44 12
45-47 22
48-50 13
This is what I have so far, not sure if I'm on the right track.
Mean: 18+7+12+22+13=72/5= 14.4
Standard deviation = 3.6, -7.4, -2.4, 7.6, 1.4
Variance = I am lost now
I really some guidance here, I have been working on this for awhile can't seem to get it. Any help and explanation please
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Given the following frequency distribution, find the mean, variance, and standard deviation. Please show all of your work.
Errors Frequency
36-38 18
39-41 7
42-44 12
45-47 22
48-50 13
----
You have to use each class mark as the representative data value
for each class:
1st class mark is (38+36)/2 = 37
Do the same for each class.
---
Mean = [37*18+40*7+41*12+46*22+49*13]/[18+7+12+22+13] = 43
std = 4.7434
variance = 4.7434^2 = 22.4998
============================
Cheers,
Stan H.
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