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Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10 PDF Download

Statistics

Statistics is a branch of mathematics that focuses on collecting, organising, analysing, interpreting, and presenting data.

Ungrouped Data

Ungrouped data is data in its original or raw form. The observations are not classified into groups.
Example: The ages of everyone present in a classroom of kindergarten kids with the teacher are as follows:

3, 3, 4, 3, 5, 4, 3, 3, 4, 3, 3, 3, 3, 4, 3, 27.

Grouped Data

  • Grouped data means that observations are organised into groups.
  • This type of data is easier to handle when there is a lot of information.

For example, a class of students got different marks in a school exam. The data is tabulated as follows:Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10This shows how many students got the particular mark range. Grouped data is easier to work with when a large amount of data is present.

Frequency

  • Frequency is the number of times a particular observation occurs in data.
  • Example: if four students have scored marks between 90 and 100, then the marks scored between 90 and 100 have a frequency of 4.
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Class Interval

  • Data can be grouped into class intervals, where all observations within that range belong to that class.
  • Class width = upper class limit – lower class limit.
  • Example: Consider a class interval 31 – 40.
    Here, the lower class limit is 31, and the upper class limit is 40.
    Hence, the size/width of the class interval 31 – 40 is calculated as follows:
    Class interval size = Upper class limit – Lower class limit
    Class interval size = 40 – 31 = 9
    Therefore, the size of the class interval is 9.

Mean

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Mean of Grouped Data (Without Class Interval)

If the data is organized in such a way that there is no class interval then we can calculate the mean by Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10where, x1, x2, x3,...... xn are the observations
f1, f2, f3, ...... fn are the respective frequencies of the given observations.
Example: Calculate mean from the following data.

Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Here, x1, x2, x3, x4, x5 are 20, 40, 60, 80, 100 respectively and f1, f2, f3, f4, f5 are 40, 60, 30, 50, 20 respectively. Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Mean of Grouped Data (With Class-Interval)

When the data is grouped in the form of class interval then the mean can be calculated by three methods.

1. Direct Method

In this method, we use a midpoint which represents the whole class. It is called the class mark. It is the average of the upper limit and the lower limit. Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Example: A teacher marks the test result of the class of 55 students for mathematics. Find the mean for the given group. Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Solution: To find the mean we need to find the mid-point or class mark for each class interval which will be the x and then by multiplying frequency and midpoint we get fx. 

Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

2. Deviation or Assumed Mean Method

If we have to calculate the large numbers then we can use this method to make our calculations easy. In this method, we choose one of the x’s as assumed mean and let it as “a”. Then we find the deviation which is the difference of assumed mean and each of the x. The rest of the method is the same as the direct method. Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Example: If we have the table of the expenditure of the company's workers in the household, then what will be the mean of their expenses?Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Solution:

As we can see that there are big values of x to calculate so we will use the assumed mean method.

Here we take 275 as the assumed mean.

Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

3. Step Deviation Method

In this method, we divide the values of d with a number "h" to make our calculations easier. Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Example: The wages of the workers are given in the table. Find the mean by step deviation method.Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Solution:

Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

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Mode

In the ungrouped data the most frequently occurring no. is the mode of the sequence, but in the grouped data we can find the class interval only which has the maximum frequency number i.e. the modal class.
The value of mode in that modal class is calculated by Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10l = lower class limit of the modal class
h = class interval size
f1 =frequency of the modal class
f0 =frequency of the preceding class
f2 = frequency of the succeeding class

Example: The table of the marks of the students of a class is given. Find the modal class and the mode.Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Solution:
Here we can see that the class interval with the highest frequency 8 is 20 – 40.
So this is our modal class.
Modal class = 20 - 40
Lower limit of modal class (l) = 20
Class interval size (h) = 20
Frequency of the modal class(f1) = 8
Frequency of the preceding class(f0) = 4
Frequency of the succeeding class (f2) = 6 Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10

Median

To find the median of a grouped data, we need to find the cumulative frequency and n/2
Then we have to find the median class, which is the class of the cumulative frequency near or greater than the value of n/2.
Cumulative Frequency is calculated by adding the frequencies of all the classes preceding the given class.
Then substitute the values in the formula Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10where l = lower limit of median class
n = no. of observations
cf = cumulative frequency of the class preceding to the median class
f = frequency of the median class
h = size of class

Example: Find the median of the given table.Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Solution:
Let’s find the n/2.
n = 20, so n/2 = 20/2 = 10
The median class is 11 - 15 as its cumulative frequency is 13 which is greater than 10. Important Definitions & Formulas: Statistics | Mathematics (Maths) Class 10Remark: The empirical relation between the three measures of central tendency is
3 Median = Mode + 2 Mean

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FAQs on Important Definitions & Formulas: Statistics - Mathematics (Maths) Class 10

1. What is the difference between mean, median, and mode in statistics?
Ans. The mean is the average of a set of numbers, calculated by adding all the values together and dividing by the number of values. The median is the middle value when the numbers are arranged in ascending order. If there is an even number of values, the median is the average of the two middle numbers. The mode is the value that appears most frequently in a data set.
2. How do you calculate the mean of a data set?
Ans. To calculate the mean, you add together all the numbers in the data set and then divide that total by the number of values. The formula is: Mean = (Sum of all values) / (Number of values).
3. When would you use the median instead of the mean?
Ans. You would use the median instead of the mean when the data set contains outliers or is skewed. The median is not affected by extreme values, making it a better measure of central tendency for non-symmetric distributions.
4. Can a data set have more than one mode?
Ans. Yes, a data set can have more than one mode. If multiple values appear with the same highest frequency, the data set is multimodal. If no value repeats, it is called a uniform distribution and has no mode.
5. How do you find the mode in a data set?
Ans. To find the mode, you count how many times each value appears in the data set. The value that occurs most frequently is the mode. If two or more values occur with the same highest frequency, all of those values are considered modes.
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