# NCERT Class 11-Math's: Exemplar Chapter –15 Statistics Part 4

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Question 2:

 Marks Obtained No. of Student

Question 3:

Calculate the mean deviation about the mean of the set of first natural numbers when is an odd number.

Question 4:

Calculate the mean deviation about the mean of the set of first natural numbers when is an even number.

Question 5:

Find the standard deviation of the first n natural numbers.

Question 6:

The mean and standard deviation of some data for the time taken to complete a test are calculated with the following results:

Number of observations , mean seconds, standard deviation seconds.

Further, another set of observations , also in seconds, is now available and we have and . Calculate the standard derivation based on all observations.

Question 7:

The mean and standard deviation of a set of observations are and , respectively while the mean and standard deviation of another set of observations are and , respectively. Show that the standard deviation of the combined set of observations is given by

Question 8:

Two sets each of observations, have the same standard derivation. The first set has a mean and the second a mean . Determine the standard deviation of the set obtained by combining the given two sets.

Question 9:

The frequency distribution:

 1

where A is a positive integer, has a variance of . Determine the value of A.

Question 10:

For the frequency distribution:

Find the standard distribution.

Question 11:

There are students in a class. The following is the frequency distribution of the marks obtained by the students in a test:

 Marks Frequency

Where is a positive integer. Determine the mean and standard deviation of the marks.

Question 12:

The mean life of a sample of bulbs was hours and the standard deviation was hours. A second sample of bulbs has a mean life of hours and standard deviation hours. Find the overall standard deviation.