Class Interval	Frequency
60 - 64	2
65 - 69	3
70 - 74	6
75 - 79	11
80 - 84	8
85 - 89	7
90 - 94	2
95 - 99	1

The table shows the distribution of marks scored by students in an examination. Calculate, correct to 2 decimal places, the

(a) mean ; (b) standard deviation of the distribution.