A Quаlity Anаlyst wаnts tо cоnstruct a cоntrol chart for determining whether errors in bank transactions are under control. She looked at samples of 1000 transactions each week, for four weeks in a row. A transaction was considered defective, if the analyst detected any error in the transaction. Week Total Defectives 1 15 2 50 3 65 4 25 What is the standard deviation of the sample proportions of defective transactions?