# 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?

**Answer**:

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)

**Answer**:

(B) Is the correct answer

**Question 8**:

Variance of the data is . Then variance of will be

(A)

(B)

(C)

(D)

**Answer**:

(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)

**Answer**:

(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 |

**Answer**: