Math Help - confidence intervals

1. confidence intervals

A random variable X has poisson distribution with parameter u(greek letter mu). A sample of 200 observations from this distribution has a mean equal to 3.4. Construct an approximate 90% confidence interval for u.

2. Originally Posted by zami
A random variable X has poisson distribution with parameter u(greek letter mu). A sample of 200 observations from this distribution has a mean equal to 3.4. Construct an approximate 90% confidence interval for u.

3. I"m not sure how to construct an interval for a Poisson distribution.
so far i have

p(x)= (µ^x e(-µ))/x! with µ=3.4 also the z value at 90% is 1.282

Where do I go from there?