Question: Poisson Distribution Values in Probability/Statistics

I am new to the Maple v.11 world and trying to figure out how to do things. I'm getting lost with the instructions in the help screens. Here is the problem: Can somebody show me how to enter this into Maple. Find the probability of an observation falling within one standard deviation of the mean. A Poisson distribution with [lambda]=16. Two other questions are normal distribution with mean=20, and a gamma distribution with [alpha]=4 and [theta]=5. I'm sure that if I can figure out one of the problems, I can figure out the others. Somebody please show me how to enter the problem into Maple.
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