The number of lightening strikes on a square kilometer of open ground in a year has mean 6 and standard deviation 2.

The number of lightening strikes on a square kilometer of open ground in a year has mean 6 and standard deviation 2.4. The National Lightening Detection Network uses automatic sensors to watch for lightening in a sample of 10 square kilometers. What is the probability that the average number of lightning strikes per square kilometer per year for 10 randomly chosen square kilometer is 3.6 or less.