" 4.(i) If "^(20)C_(r)=^(20)C_(r+6)," find "r

If .^(22)C_(r+4)=^(22)C_(r+2) , find r.

(i) If .^(20)C_(r)=.^(20)C_(r+6) , find r. (ii) If .^(18)C_(r)=.^(18)C_(r+2) , find .^(r)C_(5) .

(i) If ""^(5)P_(r)=2xx""^(6)P_(r-1) , find r. (ii) If ""^(20)P_(r)=13xx""^(20)P_(r-1) , find r. (iii) If ""^(11)P_(r)=""^(12)P_(r-1) , find r.

""^(20)C_(r) =""^(20)C_(r-10), then find the value of ""^(18)C_(r)

If .^(20)C_(r)=.^(20)C_(r-10) then find the value of .^(17)C_(r) .

If .^(20)C_(r+1)=.^(20)C_(r-1) then find the value of .^(10)C_(r) .

If ""^(20)C_(r)=""^(20)C_(r-10) , then ""^(18)C_(r) is equal to

If ^(20)C_(r+1)=^(20)C_(r-1), then r is equal to a.10 b.11 c.19d.12