## Elementary Statistics (12th Edition)

$P(X=20)={30\choose 20} \cdot (0.72)^{20}\cdot (0.28)^{10}=0.1247.$ $P(X\leq20)\geq P(X=20)=0.1247$, therefore it's probability will be quite big (bigger than 0.05), therefore it is not an unusually low number.