The frequency distribution of marks (out of 40) obtained by 30 students is given below:
Marks (class interval): 0 – 10 | 10 – 20 | 20 – 30 | 30 – 40
Frequency: 5 | 8 | 12 | 5
Find the arithmetic mean of the marks (correct to one decimal place).
(a) 25.7
(b) 20.7
(c) 20.0
(d) 22.1