3.3 Integers
People are sometimes confused by negative numbers when they first encounter them. How can I have a negative amount of anything? I can’t physically have fewer than no apples, can I?
To get around this, we introduce the idea that a positive number of things or amount of money means something that you yourself have. A negative number or amount means what you owe someone else.
If you have $100 or €100 or ¥100 and you write a check or pay a bill electronically for 120, one of two things will likely happen. The first option is for the payment to fail and your bank may charge you a fee. The second is that the bank will pay the full amount, let you know that you are overdrawn, and charge you a fee. You will then need to pay the amount overdrawn quickly or have it paid from some other account.
Whatever currency you used, you started with 100 and ended up with −20 before repayment. You owed the bank 20. If you deposit 200 in your account...
