Here's a question for you all. 

Max borrow money of 500bucks from his Dad and 500bucks from his Mum. With a total of 1k, he buy a shoe that cost 970bucks. With the balance of 30bucks, he return to his dad 10buck, return his mum 10bucks and he kept the balance 10bucks.  Max now owe his dad 490bucks and owe his mum 490bucks. 490 + 490= 980bucks and adding the money he kept for himself(10bucks) yet, with a total of 990bucks. 

Where is the 10bucks gone???

Stay free to tell me why will it happen yea. =)