solve: P(X=3) = (2/3) P(X=4)
In a Poisson distribution, the probability P of x successes is e^-m*m^x/x!, where m is the mean.
So if x=3, P=e^-m*m^3/3! and if x=4, P=e^-m*m^4/4!. If P(3)=(2/3)P(4), then m^3/6=(2/3)*m^4/24,
The standard deviation=sqrt(variance), and in a Poisson distribution, variance=mean,
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