P,Q,R,S and T sit on five chairs facing north R will sit only on the left most chair, and Q will not sit any  where to the left of P. In how many ways can they be seated
 

R will sit on seat – 1 and Q will sit somewhere to the right of P.
     These are three ways
   i) P on 2, so Q can be seated on 3,4 or 5 and the remaining can be seated on two chairs in 2-ways
   ii) P on 2, so Q can be seated on 4 or 5
   iii) P on 4, so Q will be on 5
     Total no of ways = 6+4+2 = 12