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JEE Main202127 Aug 2021Morning ShiftMathematicsBinomial TheoremActual

∑ k = 0 20 C k 20 2 is equal to

Options

  1. AC 21 40
  2. BC 20 41
  3. CC 20 40
  4. DC 19 40

Correct answer

C. C 20 40

Step-by-step solution

∑ k = 0 20 C k 20 2 = ∑ k = 0 20 C k 20 . C 20 - k 20 Sum of suffix is constant so summation will be C 20 40

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