If the classes of a frequency distribution are 1 - 10, 11 - 20, 21 - 30, …., 51 - 60, then the size of each class is

1. 9

2. 10

3. 11

4. 5.5

If the classes of a frequency distribution are 1 - 10, 11 - 20, 21 - 30, ….., 61 - 70, then the upper limit of the class 11 - 20 is

1. 20

2. 21

3. 19.5

4. 20.5

In the formula : x̄ = a + $\dfrac{Σ f$idi}{Σ f_i} for finding the mean of the grouped data, d_i's are deviations from a (assumed mean) of

1. lower limits of the classes

2. upper limits of the classes

3. mid-points of the classes

4. frequencies of the classes

Construction of a cumulative frequency distribution table is useful in determining the

1. mean

2. median

3. mode

4. all the three measures