A binomial distribution has mean 6 and variance 4.2. What are $n$ and $p$?

Explanation

1. 01

   $q = \frac{npq}{np} = \frac{4.2}{6} = 0.7$, so $p = 0.3$.

2. 02

   $n = \frac{6}{0.3} = 20$.