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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Statistics

NDA 2025 · Mathematics · Statistics

Consider the following for the two (02) items that follow: The sum...

Consider the following for the two (02) items that follow:
The sum and the sum of squares of the observations corresponding to length XX (in cm) and weight YY (in gm) of 50 tropical tubers are given as ΣX=200\Sigma X = 200, ΣY=250\Sigma Y = 250, ΣX2=900\Sigma X^2 = 900 and ΣY2=1400\Sigma Y^2 = 1400.

Which one of the following is correct?

Options

  1. AVariance (X)(X) > Variance (Y)(Y)
  2. BVariance (X)(X) < Variance (Y)(Y)
  3. CVariance (X)(X) = Variance (Y)(Y)
  4. DCannot be determined from the given data

Correct answer

B. Variance (X)(X) < Variance (Y)(Y)

Step-by-step solution

Given n=50n = 50, ΣX=200\Sigma X = 200, ΣY=250\Sigma Y = 250, ΣX2=900\Sigma X^2 = 900, and ΣY2=1400\Sigma Y^2 = 1400.

The variance of XX is calculated as:
Var(X)=ΣX2n−(ΣXn)2\text{Var}(X) = \dfrac{\Sigma X^2}{n} - \left(\dfrac{\Sigma X}{n}\right)^2
Var(X)=90050−(20050)2\text{Var}(X) = \dfrac{900}{50} - \left(\dfrac{200}{50}\right)^2
Var(X)=18−(4)2=18−16=2\text{Var}(X) = 18 - (4)^2 = 18 - 16 = 2

The variance of YY is calculated as:
Var(Y)=ΣY2n−(ΣYn)2\text{Var}(Y) = \dfrac{\Sigma Y^2}{n} - \left(\dfrac{\Sigma Y}{n}\right)^2
Var(Y)=140050−(25050)2\text{Var}(Y) = \dfrac{1400}{50} - \left(\dfrac{250}{50}\right)^2
Var(Y)=28−(5)2=28−25=3\text{Var}(Y) = 28 - (5)^2 = 28 - 25 = 3

Comparing the variances, we get Var(X)<Var(Y)\text{Var}(X) < \text{Var}(Y).

Answer: Variance (X)(X) < Variance (Y)(Y)
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