x number of betfair points and £y profit in a week. And assuming an account is in profit and is just eligible for the premium charge (i.e £1000 allowance used up and previous charges account for exactly 20% of previous profit). Would it then be true that....
If (x/10)/y=z then if z is less than 0.2 then the account would be charged a premium charge of (0.2-z)*y
irony Or does that over simplify the whole calculation?? /irony