# NCERT Class 11-Math՚s: Exemplar Chapter – 15 Statistics Part 3 (For CBSE, ICSE, IAS, NET, NRA 2023)

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Question 6:

Life of bulbs produced by two factories A and B are given below:

 Length of life (in hours) Factory A(Number of bulbs) Factory B(Number of bulbs)

The bulbs of which factory are more consistent from the point of view of length of life?

Here , let A (assumed mean) .

 Length of life(in hours) Mid values Factory A Factory B

For factory A

Mean

Therefore, Coefficient of variation

For factory B

Mean

Therefore, Coefficient of variation

Since . of factory . of factory Factory B has more variability which means bulbs of factory A are more consistent.

## Objective Type Questions

### Choose the Correct Answer Out of the Four Options Given Against Each of the Examples 7 to 9 (M. C. Q.)

Question 7:

The mean deviation of the data from the mean is

(A)

(B)

(C)

(D)

(B) Is the correct answer

Question 8:

Variance of the data is . Then variance of will be

(A)

(B)

(C)

(D)

(C) Is the correct answer.

When each observation is multiplied by , then variance is also multiplied by .

Question 9:

A set of values has standard deviation . The standard deviation of n values will be

(A)

(B)

(C)

(D)

(A) Is correct answer.

If each observation is increased by a constant , then standard deviation is unchanged.

## 15.3 EXERCISE

### Short Answer Type

Question 1:

Find the mean deviation about the mean of the distribution:

 Size Frequency