Andrew is a quality control inspector at a clothing factory. At the end of each day, he checks the number of imperfections found in cotton sweaters. The table below represents the probability density function for the random variable X, the number of imperfections found in cotton sweaters per day. Find the standard deviation of X.

Round the final answer to two decimal places.
x
P(X = x)
0
1/6
1
1/6
4
1/3
7
1/3