Age of teachers of a school varies from 24 years to 72 years. Rishabh has to make a grouped frequency distribution table of age of teachers. Which among the following class intervals of age will be most appropriate to make meaningful conclusion in less time and effort?

1. 24 - 26, 26 - 28, 28 - 30, and so on

2. 24 - 30, 30 - 36, 36 - 42, and so on

3. 24 - 48, 48 - 72

4. none of these

The distribution of marks of students of a class in a test is shown in the table below.

Which of the following statements are correct?

(i) We can definitely say that no one scored 60 marks.

(ii) The number of students who got at least 30 marks is 12.

1. only (i)

2. only (ii)

3. both (i) and (ii)

4. none of these

The class mark of a class-interval is 'a'. If its lower limit is a-b, then its upper limit is :

1. a + b

2. ab

3. b-a

4. 2b