The Missing $1

You borrowed $50 from A and $50 from B. (Total $100) - Asset = $100
You bought a pair of shoes for $97. (Left $3) - Asset = $97 shoes + $3
You returned $1 to A, $1 to B and kept the last $1 for yourself.
Now you owe $49 to A and $49 to B. - Liability
$49 + $49 = $98 + the $1 you kept. - Liability + Asset =

Total = $99 RUBBISH!

WHERE'S THE MISSING $1!?!?!

*John Zhou's student gave him this question. I'm spreading it around bcos I CANT ANSWER!!*

*YL has kindly provided the correct way of explanation. See the green text on top. If I were to explain, I'll jus tell you wat exists and wat doesnt. N to think that I'm taking ACCOUNTS..*

Simplified explanation
Liability is minus, Asset is plus.
$50 + $50 = $100 = -$100 (Liability)
$97 shoes + $3 = $100 = +$100 (Asset)
Returning $1 each to A and B
-$100 + $2 = -$98 (Liability)
$97 shoes + $1 = +$98 (Asset)
Therefore the -$98 shouldnt be treated as a positive.
-$98 + $1 = -$97 and not $99
-$97 = $97 shoes

Balanced!