The Variance

In the box below, please enter the variance of the random variable given above, then click on the “Check your answer!” button. Please round your answer to the ten-thousandths place.

Your guess:

You got the correct answer of 2.2131. Congratulations!

Unfortunately, your answer was not correct. Either try again or click on “Show Solution” below to see how to obtain the correct answer.

Show Formula

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Here is the formula you can use to calculate the variance of X.

In this formula, there are several symbols to know:

Show Solution

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Thus, the variance of this random variable is 2.2131.

Show the R Code

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Copy and paste the following code into your R script window, then run it from there.

In the R output, the number given after running the final line above is the variance of the distribution. (What does the variable Ex represent?) Note that R will give you results that are more accurate and more precise than doing the calculations by hand. As such, these computer-calculated values may differ slightly from those you calculate by hand.

Show the Excel Code

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Copy and paste the following code into your Excel spreadsheet window, making sure the value x ends up in A1 after pasting.

When copying this table to Excel, you may want to highlight this note. It seems to help ensure that the code starts in cell A1.