Q14 of 25 Page 8

Prove that 3r nCr = 4n .


L.H.S = 30C(n,0) + 31 C(n,1) + 32 C(n,2) + --- 3r(n, r) + --- +3n C(n, n) 
        = C(n,0) + C(n,1) 31 + C(n,2) 32 + C(n,3) 33 + --- +C(n,n)3n
This is in the form of (1+3)n  
        = (1+3)n = 4n = R.H.S

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