So here is the situation.

You find shirt which costs 97$. You loan 50$ from your mom and 50$ from you dad. You buy shirt and get 3$ back. You give 1$ to dad and 1$ to mom 1$ left for yourself.

Now you own 49$ to your dad and 49$ to your mom, 49$ + 49$ = 98$
And you have that one dollar so, 98$ + 1$ = 99$

Now that one dollar disappeared to somewhere. ;]