To monitor the proportion of green M&M's in packages of M&M's, a quality control manager picked at random 20 M&M packages, each with 300 M&M's in them. The manager computed the proportion of green M&M's across all these packages as 0.15. What is the standard deviation of the sampling process? Note: Each package represents a randomly selected sample. Round the final answer to three decimal places.
Select one:
a. 0.021
b. 0.079
c. 0.005
d. 0.357