In a grouped frequency distribution, the mid-values of the classes are used to measure which of the following central tendency?

1. median

2. mode

3. mean

4. all of these

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

Construct the following frequency distribution :

The upper limit of the median class is

1. 17

2. 17.5

3. 18

4. 18.5

For the following distribution :

The sum of lower limits of the median class and modal class is

1. 15

2. 25

3. 30

4. 35