Why do you need numbers less than zero?

Answer 1

Math is based off of theoretical thinking. In order to think in terms of theory one must come up with (in this case) theoretical numbers. There can't be negative three apples but you can take 3 apples AWAY from 5 apples and get 2. 5-3=2

The three is not only taking away from the previous number, but it can also be expressed as: -3

Answer #2:

Without negative numbers, you'd have a real problem

trying to talk about . . .

• any Celsius temperature colder than ice
• any Fahrenheit temperature more than 32 degrees colder than ice
• the acceleration of a car that's slowing down
• the electrostatic force of attraction between two positive charges
• the apparent weight of a beach-ball when it's at the bottom of the pool
• the rate of climb of a 747 within a half-hour before it lands in Chicago
• the balance in your checking account when you're overdrawn
• the balance on your credit card when you paid $10 more than you owed
• the voltage between the green wire and the white wire, during 81/3 milliseconds out of every 162/3