A problem by Abhimanyu Bambhaniya

Level pending

If 1 <= r<= (n-1) then n-1 C{ r} +n-2 C{ r}+ n-3 C{ r}+........r C{ r} equals-

(1) n C{ r} (2)n C{ r+1}

(3) n+1 C_{ r} (4) None of these

HINT n C_{r} = n!/(n-r)!r!

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