First you simplify 2 3/5, which can be 2.6. You will find half of it so 2.6 divided by 2 equals 1.3. She traveled 1.3 miles or 1 3/10 miles before she stopped.
Assume a binomial distribution. Then the mean of the distribution is , where is the number of people taken in a sample and is the probability of the mutation occurring in any given person, and the standard deviation is . Then in this case, the standard deviation is .