Comprehension

Consider the following for the two (02) items that follow:
The sum and the sum of squares of the observations corresponding to length X (in cm) and weight Y (in gm) of 50 tropical tubers are given as \(\Sigma X = 200$, \Sigma Y = 250, \Sigma X^2 = 900 and \Sigma Y^2 = 1400\)

Which one of the following is correct?

This question was previously asked in
NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. Variance (X) > Variance (Y)
  2. Variance (X) < Variance (Y)
  3. Variance (X) = Variance (Y)
  4. Cannot be determined from the given data

Answer (Detailed Solution Below)

Option 2 : Variance (X) < Variance (Y)
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Detailed Solution

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Calculation:

Given,

The sum and sum of squares of the observations corresponding to length X in cm and weight Y in gm of 50 tropical tubers are given as:
\(\Sigma X\) = 200, \(\Sigma Y\) = 250, \(\Sigma X^2\)= 900, \(\Sigma Y^2\) = 1400 

The formula for variance is:

\( \text{Variance} = \frac{\Sigma X^2}{N} - \left( \frac{\Sigma X}{N} \right)^2 \)

Where N = 50 is the number of observations.

Variance of X:

\( \text{Variance of } X = \frac{\Sigma X^2}{N} - \left( \frac{\Sigma X}{N} \right)^2 \)

Substituting the given values:

\( \text{Variance of } X = \frac{900}{50} - \left( \frac{200}{50} \right)^2 \)

\( \text{Variance of } X = 18 - 16 = 2 \)

Variance of Y:

\( \text{Variance of } Y = \frac{\Sigma Y^2}{N} - \left( \frac{\Sigma Y}{N} \right)^2 \)

Substituting the given values:

\( \text{Variance of } Y = \frac{1400}{50} - \left( \frac{250}{50} \right)^2 \)

\( \text{Variance of } Y = 28 - 25 = 3 \)

Conclusion:

\( \text{Variance of } X < \text{Variance of } Y \)

Hence, the correct answer is Option 2.

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