Question 1

What is the range of the data: 15, 6, 12, 20, 9, 4, 30, 18?

Accepted Answer

The range of a set of observations is the difference between the maximum and minimum values in the data. Here, the maximum value is 30 and the minimum value is 4. Range = Maximum value - Minimum value = 30 - 4 = 26.

Question 2

The class mark of the class interval 10-25 is:

Accepted Answer

The class mark of a class interval is calculated as (Upper limit + Lower limit) / 2. For the interval 10-25, Class mark = (25 + 10) / 2 = 35 / 2 = 17.5.

Question 3

If the mean of observations x, x+2, x+4, x+6, and x+8 is 11, then the value of x is:

Accepted Answer

Mean = Sum of observations / Number of observations. Sum = x + (x+2) + (x+4) + (x+6) + (x+8) = 5x + 20. Mean = (5x + 20) / 5 = x + 4. Given mean = 11, so x + 4 = 11 => x = 7.

Question 4

What is the mode of the data: 2, 3, 4, 5, 0, 2, 3, 4, 3, 5, 2, 3?

Accepted Answer

The mode is the observation that occurs most frequently. Counting frequencies: 0 appears 1 time, 2 appears 3 times, 3 appears 4 times, 4 appears 2 times, 5 appears 2 times. The number 3 has the highest frequency (4), so the mode is 3.

Question 5

For the following data, 14, 25, 14, 28, 18, 17, 18, 14, 23, 22, 14, 18, the number of times 14 occurs is:

Accepted Answer

Counting the occurrences of 14 in the given data set (14, 25, 14, 28, 18, 17, 18, 14, 23, 22, 14, 18), we find it appears 4 times.

Statistics — NCERT Class 9 Mathematics Important Questions & Revision Notes