The mean or average of a number of observations is the sum of the value of all the observations divided by the total number of observations.
Definition: If are n values of a variable X , then the arithmetic mean or simply the mean of these values is denoted and is defined as
Here, the symbol denotes the sum .
In other words, the arithmetic mean of a set of observations is equal to their sum divided by the total number of observations.
Illustration 1: If the heights of 5 persons are 144 cm, 152 cm, 151 cm, 158 cm and 155 cm respectively. Find the mean height.
Solution: To calculate mean we will find the sum of observations and divide it with number of observations
Illustration 2: The mean of 6, 10, X and 12 is 8. Find the value of x.
Solution: Using the definition
So , the value of x is 4.
Illustration: The marks obtained by 30 students of Class X of a certain school in a Mathematics paper consisting of 100 marks are presented in table below. Find the mean of the marks obtained by the students.
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Right Option : C | |||||||||||||||||||||||||||||||
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If each entry of a data is increased by 5, then the arithmetic mean ____________________ | |||
Right Option : B | |||
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20 years ago, when my parents got married, their average age was 23 years, now the average of my family, consisting of myself and my parents only is 35 years. My present age is | |||
Right Option : D | |||
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