If X, the Time (In Minutes)to Complete an Oil Change $\le$

Multiple Choice

If x, the time (in minutes) to complete an oil change job at a certain auto service station, is uniformly distributed over the interval 20 to 30, inclusively (20 $\le$ x $\le$ 30) , then the standard deviation of this distribution is ___.

A) unknown
B) 8.33
C) 0.833
D) 2.89
E) 1.89