1.

If `""^(n)C_(0), ""^(n)C_(1),..., ""^(n)C_(n) ` denote the binomial coefficients in the expansion of `(1 + x)^(n) and p + q = 1` , then ` sum_(r=0)^(n) ""r.^(n)C_(r) p^(r) q^(n-r) = `A. nB. npC. npqD. none of these

Answer» Correct Answer - b
(i) We have,
`sum_(r=1)^(n) r. ""^(n)C_(r) p^(r)q^(n-r)`
` sum_(r=1)^(n)r.(n)/(r)""^(n-1)C_(r-1) p.p^(r-1)q^((n-1)-(r -1))`
` = np {sum_(x=1)^(n) ""^(n-1)C_(r-1) p^(r - 1) q^((n-1)-(r-1))}`
` = np (q + p)^(n-1) [ because (q + p)^(n) = sum _(r=0)^(n) ""^(n) C_(r)p^(r) q^(n-r)]`
`= np [ because p + q = 1]` .


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