Jumbo shrimp are those that require $10-15$ shrimp to make a pound. Suppose that the number of jumbo shrimp in a 1 -pound bag averages $\mu=12.5$ with a standard deviation of $\sigma=1$, and forms a normal distribution. What is the probability of randomly picking a sample of $n=251$-pound bags that average more than $M=13$ shrimp per bag?