Can someone provide me with some assistance in answering this question..

Question

A company manufacturers batteries in BATCHES of 18 and there is a 3% rate of defect. Find the standard deviation for the number of defects per batch.

The probability of a defect is p = 0.03

The mean number of defects in a batch of N = 18 is m = p N = 0.03 x 18 = 0.54

The standard deviation of the number of defects in a batch of 18 is
sigma = sqrt [N p (1-p)] = 0.72, which actually exceeds the mean value in this case.

Answer 1

Can you explain how you got the standard deviation of the number of defects in a batch of 18 is sigma=sqrt[N p (1-p)]=0.72. IN OTHER WORDS HOW DID YOU GET 0.72