[SOLVED] A Chebyshev interval with a poisson distribution Geophysicists determine the age of a zircon by counting the number of uranium fission tracks on a polished surface; the number of these uranium fission tracks on this surface follows a Possion distribution. A particular zircon is of such an age that the average number of tracks per square centimeter is seven. Give an interval that will include at least 60% of the sample values of fission track counts obtained from a large number of square centimeter samples. I know this problem require chebyshevs theorem, but I don't have the standard deviation. How do I figure this out?