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Question

1.nC1 + 2.nC2 + 3.nC3 + ….+ n.nCn is equal to

  1. fraction numerator n open parentheses n plus 1 close parentheses over denominator n end fraction.2 to the power of n end exponent    
  2. 2 to the power of n plus 1 end exponent minus 3    
  3. n.2 to the power of n minus 1 end exponent    
  4. none of these.    

The correct answer is: n.2 to the power of n minus 1 end exponent


    Since r. nCr = n.n-1Cr-1
    \ reqd. sum
    equals n open square brackets n minus 1 C subscript 0 end subscript plus to the power of n minus 1 end exponent C subscript 1 end subscript plus to the power of n minus 1 end exponent C subscript 2 end subscript plus.... plus to the power of n minus 1 end exponent C subscript n minus 1 end subscript close square brackets equals n.2 to the power of n minus 1 end exponent

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