For a Poisson distribution, find P(3), given λ =1/2.

The correct answer is Option (2) → 0.013

For a Poisson distribution,

$P(r) =\frac{λ^re^{-λ}}{r!}$

$P(3)=\frac{(\frac{1}{2})^3.e^{-0.5}}{3!}=\frac{\frac{1}{8}×0.607}{6}$   [$∵e^{-0.5}=0.607$, from table]

$=\frac{0.607}{48}= 0.013$