Your mother gave you Dollar 300 to buy some household goodies from the market. The goodies cost just Dollar 295. So, the shopkeeper gave you Dollar 5 back. Seeking the opportunity to buy something, you bought two candies for yourself worth Dollar 2 and gave back Dollar 3 to your mother.
Now, your mother gave you Dollar 300 and got back Dollar 3 back. In this manner, she paid just Dollar 297 on the goodies and you spent Dollar 2 on candies.
So where is the remaining one Dollar ?