Math Help - Poisson's distribution problem

1. Poisson's distribution problem

If a random variable is Poisson's distributed with a mean of 5.2 determine (a) standard deviation (b) the probability that random variable will have a value of three or less (c) the probability that random variable will have a value of more than 6 .

2. st dev=square root of 5.2

$P(X\le 3)= P(X=0)+...+P(X=3)$

where $P(X=x)={e^{-5.2}(5.2)^x\over x!}$

$P(X>6)= 1-\biggl(P(X=0)+...+P(X=6)\biggr)$

3. Thank you so much!Hey I have just one more problem on Control charts,Can I post it in this forum?