what they have what you have what the store has what you owe them
100 0 0 0
0 3 97 100
2 1 97 98
they have 98 and you owe them 98.
nothing is missing.
you cannot add the 1 to the 98.
they are 2 different things.
you owe them 98 because you kept the 1.
give them the 1 and you owe them 97 which is the price of the shirt.
there is nothing missing.
you do not owe them 99.
you owe them 98.
it's the 100 minus the 2 that you gave them.
that leaves 98.
the 1 that you kept is part of the 98 that you still owe them.