Placing events on the probability line
How do we measure how likely something is to happen? Mathematicians use a number called probability.
Every probability lives on a number line that goes from zero to one.
Zero means impossible. The event can never, ever happen.
One means certain. The event is guaranteed to happen.
One-half is right in the middle — the event is equally likely to happen or not.
Roll a seven on a regular six-sided die? That's impossible — probability zero.
Roll a one? There's only one way out of six, so the probability is one-sixth, about 0.17 — unlikely.
Roll an even number? Three of six sides work, so the probability is one-half — equally likely.
Roll less than six? Five of six sides work, so the probability is five-sixths, about 0.83 — likely.
Roll any number from one to six? That's certain — probability one.
The closer a probability is to zero, the less likely. The closer to one, the more likely.
Every probability is a number between zero and one — that's all you need to compare how likely things are.