We first determine the z-score associated with x = 4.4. Given the mean of 4.4 minutes and the standard deviation of 0.4 minutes, since the value of x is exactly equal to the mean, this is equivalent to a z-score of 0. By definition on the normal distribution, half of the distribution should be above the mean, so there should be 50% who are on hold for more than 4.4 minutes.
