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Question

What is the mean of the following distribution?
Marks1936606985
No. of Students6362591770

The correct answer is

52

Solution :- 

Calculating Mean from Marks and Frequency Data

To find the mean of a frequency distribution, we need to sum the product of each value (Marks) and its corresponding frequency (No. of Students) and then divide by the total number of observations (total frequency).

The formula for the mean ($\bar{x}$) of a frequency distribution is:

$$ \bar{x} = \frac{\sum (f \cdot x)}{\sum f} $$

Where:

  • $x$ represents the values (Marks).
  • $f$ represents the frequencies (No. of Students).
  • $\sum (f \cdot x)$ is the sum of the products of each value and its frequency.
  • $\sum f$ is the sum of all frequencies (total number of students).

Data Organization and Calculation

First, let's organize the given data into a table and calculate the product ($f \cdot x$) for each row:

Marks ($x$)No. of Students ($f$)Product ($f \cdot x$)
196$19 \times 6 = 114$
363$36 \times 3 = 108$
606$60 \times 6 = 360$
692$69 \times 2 = 138$
855$85 \times 5 = 425$


 

Summing the Values

Next, we calculate the sum of the 'No. of Students' column ($\sum f$) and the sum of the 'Product ($f \cdot x$)' column ($\sum (f \cdot x)$).

  • Total No. of Students ($\sum f$): $$ \sum f = 6 + 3 + 6 + 2 + 5 = 22 $$
  • Sum of Products ($\sum (f \cdot x)$): $$ \sum (f \cdot x) = 114 + 108 + 360 + 138 + 425 = 1145 $$

Mean Calculation

Finally, we apply the formula using the sums calculated above:

$$ \bar{x} = \frac{\sum (f \cdot x)}{\sum f} = \frac{1145}{22} $$

Performing the division:

$$ \bar{x} \approx 52.045 $$

Rounding the result to the nearest whole number, the mean marks are approximately 52.

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Important Questions from Measures of Central Tendency

  1. The mean of five numbers is 30. If one number is excluded, their mean becomes 28. The excluded number is

  2. The ‘less than’ ogive curve and the ‘more than’ ogive curve intersect at

  3. The observations 4, 1, 4, 3, 6, 2, 1, 3, 4, 5, 1, 6 are outputs of 12 dices thrown simultaneously. If m and M are means of lowest 8 observations and highest 4 observations respectively, then what is (2m + M) equal to ?  

  4. The mean of the series x 1, x 2… x nis X̅. If x 2­ is replaced by λ, then what is the new mean?

  5. The mean of a group of 100 observations was found to be 20. Later it was found that four observations were incorrect, which were recorded as 21, 21, 18 and 20. What is the mean if the incorrect observations are omitted?

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