a) A student travels by bus to get to school. On twenty-two separate occasions, she makes a note of the length of time she has to wait for the bus to arrive. The results are shown below in table Q9a:
Waiting time (mins)
time in Minutes:4 5 6 7 8 9
No. of times :2 4 7 6 2 1
Calculate the mean and standard deviation of the waiting time.
I can do the mean, but wtf the standard deviation.