You're given 50 gold coins before your big journey,
but you decide to leave 25 of them at home before leaving.
On the first day you spend 20% the gold you brought on food and
you give 10 of the remaining coins to a beggar who has nothing.
The king now claims 20% of all gold in the country,
which everyone pays in person instantly.
the next day the beggar, who didn't buy a thing,
gives you all his gold back,
because he felt guilty for taking it.
How many gold coins do you have
left for the rest of your journey ?