" यदि (If) "20P_(r)=6840,r

If ^20P_r=6840 , find r.

If "^(20)P_r=6840 , find r.

Find the value of n if ""^54P_(r+3)=6840 xx ""^54P_(r+6)

(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.

If ""^(56)P_(r+6) : ""^(54)P_(r+3)= 30800, then r is

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

Find r if P (20,r)=13.P(20,r-1).

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