The frequency distribution of the marks obtained by students in a Science examination is given below:
 

Marks	5-15	15-25	25-35	35-45
Number of students	20	30	30	20

What is the arithmetic mean?

If P(A) = 0.3 , P(B) = 0.4 and P( A |B)=0.5, then what is the value P( B |A) ?
 

If P(A) = 1/3 , P(B) = 1/2 and $ P(A\cap B)=1/4$ , then what is the value of $P(\overline{A}\cup B)$ ?

Consider the following statements:

I. Mean and variance have the same unit of measurement.

II. Mean deviation and standard deviation have the same unit of measurement.

Which of the statements given above is/are correct?