The value of `sum_(r=0)^9 (^10C_r)/(^10C_r+^10C_(r+1))` is equal to

The value of sum_(r=1)^(10)r.r! is

The value of sum_(r=0)^(20)(-1)^(r )(""^(50)C_(r))/(r+2) is equal to

The value of sum_(r=0)^(20)(-1)^(r )(""^(50)C_(r))/(r+2) is equal to

The value of sum_(r=1)^(10)r(n C_(r))/(n C_(r-1)) =

the value of 40c_(31)+sum_(r=0)^(10)(C_(10+r)^(40-r)) is equal to

The value of sum_(r=0)^(10)r(C(n,r))/(C(n,r-1))=

The value of sum_(r=0)^(10)(r)^(20)C_(r) is equal to 20(2^(18)+^(19)C_(10)) b.10(2^(18)+^(19)C_(10)) c.20(2^(18)+^(19)C_(11)) d.10(2^(18)+^(19)C_(11))

The value of sum_(r=1)^(10) r. (""^(n)C_(r))/(""^(n)C_(r-1) is equal to