Finding the standard deviation.

Question

The probability that a radish seed will germinate is 0.7. A gardener plants seeds in batches of 17. Find the standard deviation for the number of seeds germinating in each batch.

Answer 1

This is modelled using the binomial distribution.  The formula for the standard deviation is

sqrt(n*p*q), where n is the number of trials, p is the probability of a success, and q is the probability of failure = 1-p

If you prefer, you may write this formula as sqrt(n*p*(1-p))

Thus, the solution to this particular problem, as n = 17, p = .7, and q = 1 - p = 1 - .7 = .3, is

sqrt(17 * .7 * .3) = sqrt(3.57) = 1.89