You see a shirt for 97 dollars.
you don't have the cash so you borrow 50 bucks from your mom and 50 bucks from your dad,
50+50=100.
so you buy the shirt and you have 3 dollars change.
you give your dad 1 dollar and your mom 1 dollar, and you keep 1 dollar.
now you owe your mom 49 dollars and your dad 49 dollars. 49+49=98 + your 1 dollar=99 dollars.
where is the missing 1 dollar?

When you paid $97.00 for the shirt you should have given each parent $48.50 for the purchase of the shirt, which would = $97.00. 

Then add the $1.00 each you returned from the change. At this point you should have $99.00 as your total. 

Finally add the $1.00 that you kept, which should give you $100.00. 

In the end you still owe your parents an additional .50 cents each for your initial purchase of the shirt.