54,31,19.5.13.75,10.875, ___________, ____________, n=n:--------------

If you look at the sequence there is no pattern easily reonizable. You have to take the 54 and subtract 31 this will give you 23 then do 31-19.5 you will get 11.5 this shows that the sequence is the number minus 1/2 of the previous subtraction. In this you subtract 23 then 11.5 then 5.75 and so on. Hope this helps you.