Integers in real life

Integers turn up in real life. Suppose you open a bank account with ₹100.

• The next day you earn ₹60 and put it in: money coming in is a credit, so the balance is ₹160.
• Then you pay an electric bill of ₹30 from the account: money going out is a debit, so the balance is ₹130.
• Next you make a big purchase for your business of ₹150, another debit. Now the balance is ₹130 - ₹150 = -₹20.

Is that possible? Yes: some banks allow a balance to go negative for a while, though they may charge interest or a fee. A balance of -₹20 means you owe the bank ₹20: it is not your money.

Your purchase helps you earn ₹200 the next day, a credit. The balance becomes -₹20 + ₹200 = ₹180. We can think of credits as positive numbers and debits as negative numbers; adding them all up gives the balance, which can be positive or negative. In general, it is better to keep a positive balance!

Heights of mountains, plateaus and deserts are measured from sea level, which is 0 m. Heights above sea level are positive numbers, and heights below sea level are negative numbers. Years work in a similar way: years Before the Common Era (BCE) count backwards, like negative numbers, and there is no year 0: 1 BCE is followed straight by 1 CE.

Temperature is measured in degrees Celsius (°C). 0°C is the freezing point of water, and temperatures colder than that are negative. Leh in Ladakh gets very cold in winter, coldest in the middle of the night. On one November day there, the readings were 14°C, 8°C, -2°C and -4°C. The warmest was 14°C and the coldest was -4°C, which is 4 degrees below freezing.