A normal distribution has a mean of 312.00 and a standard deviation of 26.45. Which interval centered at the mean has a 68% probability of containing a random value drawn from the distribution?

The first interval, or one standard deviation away from the mean, has a 68% probability that it contains a random value drawn from the distribution. This is known as the 68-95-99.7 rule, because with each additional standard deviation away from the mean, the probability increases to the value given (68, 95, 99.7) that the random value drawn will be included in the distribution.