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

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