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If .^(n+1)C(r+1):^n Cr:^(n-1)C(r-1)=11 :...

If `.^(n+1)C_(r+1):^n C_r:^(n-1)C_(r-1)=11 :6:3,` then `n r=` `20` b. `30` c. `40` d. `50`

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