You are given the following data pertaining to kilowatt hours of electricity consumed by some users in the city of Dhaka:

Consumption(in Kilowatt hours) | Number of users

20-30 |   13

30-40 | 35

40-50 | 25

50-60 | 23

60-70 | 20+X

Where X is the last digit of your University ID (i.e. 1900001). 

Estimate the following: 

a) sample variance and the sample standard deviation 

b) mean deviation 

c) coefficient of variation. 

Assume that the last digit of university id is 4