The easiest way to compute the mean absolute deviation (MAD) is to use a spreadsheet.
Place the given data set in column A.
Use the spreadsheet built in function called "AVERAGE" to find the arithmetic mean. This will add up the values and divide by the sample size. Place the result in cell C1.
For example, if there are 10 values from A1 to A10, then =AVERAGE(A1:A10) placed in cell C1 will display the mean in cell C1. Don't forget about the equal sign up front.
In column B, we subtract each value in column A from the mean we just computed. Afterward, apply absolute value to ensure the result isn't negative. For example, cell B1 will have the command =ABS(A1-$C$1) while cell B2 will have the command =ABS(A2-$C$1) and so on. Once the first command is typed in, the remaining other computations for column B are fairly quick to construct (because the spreadsheet autocompletes it for you). Review the spreadsheet help manual for more info about that.
After column B is filled out, use the function named "AVERAGE" to find the mean of the values in column B. Place this result in cell C2. This result is the MAD.