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NDA 2 2025 Maths, question 101

Topic: Statistics

Q101

What is the harmonic mean of the numbers C(10,3)C(10,3), C(10,4)C(10,4), C(10,5)C(10,5), C(10,6)C(10,6) and C(10,7)C(10,7)?

  1. (a) 3150/193150/19Correct answer
  2. (b) 4000/194000/19
  3. (c) 252252
  4. (d) 225225

Solution.

Answer: (a) 3150/193150/19

  1. The five values are 120,210,252,210,120.
  2. Their reciprocal sum is 2/120+2/210+1/252=19/630.
  3. Therefore the harmonic mean is 5/(19/630)=3150/19.