(a)[3]
Calculate the standard deviation of the times spent by people visiting this dentist.
(b)[3]
Find the probability that the time spent visiting this dentist by a randomly chosen person deviates from the mean by more than $1$ minute.
(c)[3]
Find the probability that, out of $6$ randomly selected people, more than $2$ have visits lasting longer than $10$ minutes.
(d)[5]
Find the probability that, of $35$ randomly chosen people, fewer than $16$ have visits lasting less than $8.2$ minutes.