Calculating liability from dutching a remembered selection

How do I calculate the liability in order to acheive £1 profit from a set of remembered selections?

So..for example I have remembered all selections who back price is under 10... how what is the calculation to work out the liability to win £1?

Hi
use the matching selections back book%
LIABILITY = match_b_book*(PROFIT TARGET/(100 - match_b_book))

for yours:
selections back price is less than 10
match_b_book*(1/(100 - match_b_book))

to see it in view variables you will need to execute the trigger no more often than x
or write it to a user variable 

Thanks