1.

If x, y and r are positive integers, then ""^(x)C_(r)+""^(x)C_(r-1)+""^(y)C_(1)+""^(x)C_(r-2)""^(y)C_(2)+......+""^(y)C_(r)=

Answer»

`(X!y!)/(R!)`
`((x!y!))/(r!)`
`""^(x+y)C_(r)`
`""^(XY)C_(r)`

ANSWER :C


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