Question 1188222
the mean is np=2.1 cases
variance is np(1-p)=0.63 cases^2
sd is sqrt (V)=0.79 cases
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no positive patients is 0.3^3=0.027
exactly 1 positive is 3*0.7*0.3^2 since three ways that can happen=0.189
exactly 2 positives is 3*0.7^2*0.3=0.441
exactly 3 positives is 0.7^3=0.343
Those 4 possibilities add to 1.0