If x_i's are the class marks of the class-intervals of grouped data, f_i's are the corresponding frequencies and x̄ is the mean, then Σ f_i(x_i − x̄) is equal to :

1. −1

2. 0

3. 1

4. 2

In the formula x̄ = a + h $\Big(\dfrac{\Sigma f$i ui}{\Sigma f_i}\Big) for finding the mean of grouped frequency distribution, u_i =

1. $\Big(\dfrac{x_i + a}{h}\Big)$

2. h (x_i − a)

3. $\Big(\dfrac{x_i − a}{h}\Big)$

4. $\Big(\dfrac{a − x_i}{h}\Big)$

A distribution consists of three components with frequencies 45, 40 and 15 having their means 2, 2.5 and 2 respectively. The mean of the combined distribution is :

1. 2.1

2. 2.2

3. 2.3

4. 2.4

The combined mean of three groups is 12 and the combined mean of first two groups is 3. If the first, second and third groups have 2, 3 and 5 items respectively, then the mean of third group is :

1. 10

2. 12

3. 13

4. 21