The Standard Deviation is ~0.707

Step by step:

1 2 2 4

• Identify the mean of the set as 2

• Identify the deviation of each value in the set from the mean:

1 0 0 1

• Square the deviation values

1 0 0 1

• Identify the mean of the squared deviations as 0.5

• Identify the square root of 0.5 as ~0.707