The frequency distribution of daily pocket money (in rupees) for 20 students is given below:
Mid-value (x): 2, 4, 6, 8
Frequency (f): 3, 5, 7, 5
Find the population standard deviation of the distribution, correct to two decimal places.
(a) 4.04
(b) 2.06
(c) 2.01
(d) 2.05