HELP ME TO COUNT

I'd remember that I want to buy a second hand car few times ago...its about $9700.
I came to John and borrowed some money, than he give me $5000..
Than I go to Michael and ask some money too..he gave me $5000 ..

I have $10.000 in my hand..than I have my car now...yippiiii...!!!

Still have $300 in hand..
I give back the money to John and Michael $100 each..

Still got $100 in hand..
(Fiuhhh..)

Going home..lay down on my bed..
Looking my new second hand car from the window..
Counting my debt again..

John..
$5000-$100 = $4900
Michael..
$5000-$100 = $4900

Debt Accumulation for John and Michael : $4900 + $4900 = $9800
Money in hand : $100

Wait a minute..something going wrong here..!!!

$9800 + $100 = $9900

But there was $10.000 before..
THEN WHERE IS $100..???!!!