NCERT Solutions for Class 11 Maths Chapter 13 Exercise 13.2

It is to be remembered that mean deviation should be calculated around the median if the question is silent whether to calculate it from the mean or the median. The limitation of mean deviation is that if it is calculated about the median, it is not fully reliable- when the degree of variability around the median is high. Another limitation is that mean deviation is calculated by taking absolute values and, therefore, cannot be subjected to further algebraic treatment.

To overcome the limitations of mean, mode or median, another measure was developed which called standard deviation. Standard deviation can be remembered easily if we remember that it is the square root of variance or square root of mean of sum of squared deviations taken from the mean.

The standard deviation can be calculated for the ungrouped data and grouped data as well. There are shortcut method to find variance and standard deviation. The 11th Mathematics exercise 13.2 deals with finding the standard deviation using various methods.

Example 12 of chapter 13 NCERT shows how standard deviation, variance and arithmetic mean are calculated by shortcut method or assumed mean method. Most of the examples are important for school tests or terminal exams. Last example just before the exercise 13.2 starts, is asked several times in many school exams. So, it is advised to practice all the examples for the preparation of exams.

In exercise 13.2 there are 10 questions in all. The first three question are very simple and are related to individual series. Question number 4 to 6 are related to discrete series.

Question number 7, 8, 9 are similar and related to continuous series. So, you may attempt one or two question from each group. However, you must do question number 10 because it is related to series which is not continuous. However, all these questions are simple application of the formula.