Alright smart people Let's see who will be the first one to break this down
You didn't have the cash, so you borrowed $50 from your mom and $50 from your dad.
$50 +$50 = $100
You bought the shirt and had $3 change. You gave your dad $1 and your mom $1 and kept $1 for yourself.
Now you owe your mom $49 and your dad $49.
$49 + $49 = $98 + your $1= $99.
Where is the missing $1?

This is very clever!
Here's my answer..
Really there isn't a missing dollar. You still have $1 left.
You paid mom and dad $1 each which made "you owe" them $49 each instead of $50.
If you took the $2 you paid them plus the $1 you kept for yourself that would equals the $3 change return from purchasing the shirt.
That's my answer.