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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. If X̅ = 20 is the mean of 10 observations x1, x2, ... x10; then what is the value of \(\displaystyle \sum_{i=1}^{10}\left(\frac{3 x_i-4}{5}\right) ?\) ?

  2. What is the mean of the numbers 1, 2, 3, ... 10 with frequencies 9C09C19C2 ..., 9C9, respectively?

  3. Which one of the following measures of central tendency is used in construction of index numbers?

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

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

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