Algebra II : Variance

Example Questions

Example Question #1 : Variance

Calculate the variance of the following set of values.

Explanation:

Variance is the average of the squared differences from the mean. So start by working out the mean of the set of values.

Then, for each number, subtract the mean and square the result.

The average of the results is the variance.

Example Question #2 : Variance

What is the variance of the following set of numbers?

Explanation:

Remember that the variance of a set of numbers is equal to its standard deviation squared. So if the formula for standard deviation is known to be:

Then the variance is simply , given by the following equation:

Where  is the variance, N is the number of values in the set,  is the number currently being evaluated in the summation, and  is the mean of the set. So all we must do to find the variance is determine our mean, and then sum the values given by subtracting the mean from each number in the set and squaring it, dividing the final sum by N to give us our variance. We start by determining the mean of the set:

We then find each value that will be added together by subtracting our mean from each of the numbers in our set and then squaring the result:

Looking at our formula for variance, all we must do now is add these values together and divide by N:

Example Question #1 : Variance

A set of five numbers is given as follows, where one of the numbers, , is unknown:

If the mean of the set is , what is the variance?

Explanation:

Before we can determine the variance of the set, we must first determine the value of x, our unknown. The problem tells us the mean of the set, and we know each number in the set except for x, so we can solve for x as follows:

Now that we know all the values of the set, the mean, and the number of values, we can solve for the variance using the following equation:

Where is the variance, N is the number of values in the set, is the value currently being evaluated in the set, and is the mean of the set. We start by determing the value of each term in the summation part of the formula:

Now that we now each value of the summation, all we have left to do is add them all together and divide the final result by N:

Example Question #4 : Variance

What is the variance for the values , , and ?

Explanation:

Write the formula for variance.

The value of  represents each number in the data set.

The value of  is 3, since there are 3 numbers in the data set.

Find the mean, .

Rewrite the variance formula:

Example Question #5 : Variance

Determine the variance if the standard deviation is .

Explanation:

Write the formula relationship between standard deviation and variance.

The standard deviation is the square root of variance.

Substitute the standard deviation.

Square both sides.

Example Question #1 : Variance

Evaluate the variance if the standard deviation is .

Explanation:

Write the formula for the variance.

The standard deviation is the square root of variance.

Substitute the value of standard deviation in the formula.

Square both sides.

Example Question #7 : Variance

The standard deviation of a distribution is 9. What is the variance?

Explanation:

The variance of a distribution is equal to the standard deviation squared.

Example Question #8 : Variance

Determine the population variance given the following data set:

Explanation:

To determine the variance, we will need to find the squared differences of the mean, and take the average.

Find the mean.

Subtract each number from the mean and square the quantities.

Divide this value by three.