sample variance and sample standard deviation

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Age range (years) 1-10, 11-20, 21-30, 31+ (use 35.5 as midpoint) 

# of individuals in above groups: 36, 25, 20, 10. (total 91 members)

15.9 is the mean. what is the sample variance and sample standard deviation? round answers to one decimal place.

Jan 28th, 2015

Finding sample variance

36, 25, 20, 10……..add them up


Step 2: square you answer and divide by number of terms

91*91=8281/4=2070.25……set this number aside

Step 3: Take your set of original numbers from Step 1, and square them individually,


Step 4: Subtract the amount in Step 2 from the amount in Step 3.


Step 5: Subtract 1 from the number of items in your data set.


Step 6: Divide the number in Step 4 by the number in Step 5. This gives you the variance

350.75/3=116.9,hence sample variance=116.9

Finding Sample standard deviation:


Step 7: Take the square root of your answer from Step 6


Jan 29th, 2015

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