" 5."(^20P_(r-1))/(a)=(^20P_(r))/(3)=(^20P_(r+1))/(4)" then "a=

(20P_(r-1))/(a)=(20P_(r))/(1)=(20P_(r+1))/(6) then a

(20P_(r-1))/(a)=(20P_(r))/(1)=(20_(r+1))/(6) then a=

IF ""^(20)P_(r):""^(20)P_(r-1)=15 :1 then r=

if 20C_(r-1)=20C_(r+1) then rC_(5)

If ""^(20)P_(r)=13xx""^(20)P_(r-1) find r.

If 20C_(r+1)=^20C_(r-1) , then r is equal to:

(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.

Find 'r' if : (i) ""^(5)P_(r )= ""^(6)P_(r-1) (ii) 5""^(4)P_(r )=6""^(5)P_(r-1) (iii) ""^(5)P_(r )=2""^(6)P_(r-1) (iv) ""^(10)P_(r+1): ""^(11)P_(r )=30 :11 .

If ""^(22)P_(r+1):^(20)P_(r+2)=11:52, find r.