[Sundae]

I was thinking this through when walking in the park this morning.
I think I have it straight. My problem was positing the missing number as a zero. Instead I will call it an unknown number, with only it's relationship to 15 known.

So I know the value of the goods to be more than $15. So if I was being honest I would write >£15, because the crocodile is eating the unknown LARGER figure.

And if I was being sneaky and trying to con Mr Taxman (which I would never do) I would write <$15 because the crocodile thinks $15 is better than what I really spent.

I know that's pretty much what you write Monnie, I just had to test it out for myself.

Whew. Maybe we can do long division some time. I was off school when they learned that and never did pick it up.