# If X is a Poisson variate such that $P(X-1)-P(X=2),$ then $P(X=4)=$

$\begin {array} {1 1} (1)\;\frac{1}{2e^3} & \quad (2)\;\frac{1}{3e^2} \\ (3)\;\frac{2}{3e^2} & \quad (4)\;\frac{1}{e^2} \end {array}$

$(3)\;\frac{2}{3e^2}$
answered Nov 7, 2013 by