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Square each standard deviation individually to get each variance. Add the variances, divide by the number of variances and then take the square root of that sum.

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No, independent linear variables work like this:

If X and Y are any two random variables, then mX+Y = mX + mY
If X and Y are independent random variables, then s2X+Y = s2X + s2Y

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Q: How to add standard deviations?
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Related questions

How do you subtract standard deviations?

Square the standard deviations, subtract/add them and calculate the square root of the subtraction/sum. StDV=sqrt (StDvA^2+StDvB^2)


How many standard deviations is 16.50 from the mean?

How many standard deviations is 16.50 from the mean?


What is the sum of the deviations from the mean?

The sum of standard deviations from the mean is the error.


What does normality mean in health and social care?

All minor deviations occurring with two standard deviations under the Gaussian curve are considered normal. Deviations occurring outside of two standard deviations are considered abnormal.


In a standard normal distribution 95 percent of the data is within plus standard deviations of the mean?

95% is within 2 standard deviations of the mean.


What is the standard deviation for Wechsler intelligence for children?

The mean for the WISC, like the WAIS, is 100. The deviations from 100, or standard deviations, are 15.


I have two data sets with the same number of values with means x1 and x2 and standard deviations of n1 and n2. How do you average means with standard deviations?

You can't average means with standard deviations. What are you trying to do with the two sets of data?


What is 2 standard deviations?

2 times the standard deviation!


The mean number is 14 with a standard deviation of 2.5 How many standard deviations is 16.50 from the mean?

16.5 is 1 standard deviation from the mean. If you add the mean of 14 to the 1 standard deviation of 2.5, the result is 16.5.


How many standard deviations is 19 from the mean?

That depends on what the standard deviation is.


What does STD devs stand for?

standard deviations


This tells how many standard deviations a measurement is away from the mean?

Z-Score tells how many standard deviations a measurement is away from the mean.