Question

Marks obtained	Number of students
Less than 10	3
Less than 20	7
Less than 30	13
Less than 40	16
Less than 50	21
Less than 60	27

On the basis of above table if the frequency of class interval 20 - 30 is p and of 40 - 50 is q, then the difference of p and q is
1. 1
2. 11
3. 6
4. 5

Answer 1

Correct Answer - Option 1 : 1

Concept:

The frequency of any class interval is calculated by subtracting the preceding cumulative frequency from the cumulative frequency of that class interval.

Calculation:

Marks obtained	Number of students (c.f.)	Frequency
0 - 10	3	3
10 - 20	7	7 - 3 = 5
20 - 30	13	13 - 7 = 6
30 - 40	16	16 - 13 = 3
40 - 50	21	21 - 16 = 5
50 - 60	27	27 - 21 = 6

Now, the frequency of class interval 20 - 30 is p

⇒ p = 6

Also, the frequency of class interval 40 - 50 is q

⇒ q = 5

∴ p - q = 6 - 5 = 1

Hence, the difference of p and q is 1.