I am trying to work on an effect in which the volunteer may lie. For example, suppose we have 8 options requiring 3 cards. Instead of answering truthfully the volunteer lies. Let's say the target number is 6, if they lie the outcome of the answers is 9 (an out of range and thus impossible number) simply subtract from 15 to get 6. My problem is this breaks down for the numbers 7 and 8. You will not know if they lied or not. Anyone have an inkling how to solve this?

I am afraid your approach cannot be understood without more details and one or two examples.

Thanks saxonia, I have worked it out, not as difficult as I thought. It's basically the old binary 'age'/'computer' cards but the volunteer is able to lie.

Are you aware of the work of Leo Boudreau? That might be helpful to you in finding methods for this type of effect.

Thanks Freddie, yes I am aware of Leo's work and I have now resolved my difficulty (much easier than I thought actually).

Also I did not realise that 'Magical Equations' was an open forum, will have to take care what I ask about in future.