Sergio's job is just a few bus stops away from his house. While it can be faster to take the bus to work, it's more variable, because of variations in traffic. He estimates that the commute time to work by bus is approximately normally distributed with a mean of 12 minutes and a standard deviation of 4 minutes. The commute time if he walks to work is also approximately normally distributed with a mean of 16 minutes with a standard deviation of 1 minute. Calculate and interpret the mean of the difference d = b - w in the time it would take Sergio to get to work on a randomly selected day?
