If x, the time (in minutes) to complete an oil change at a certain auto service station, is uniformly distributed over the interval 20 to 30, inclusively (20 ≤ x ≤ 30), then the probability that an oil change is completed in 25 to 28 minutes, inclusively, i.e., p(25 ≤ x ≤ 28) is __________________.
