How Likely Is That?

Shelly Berman shelly@mathforum.org

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We use numbers to tell the measures of many different things - time, length, money, and weight are examples.

We can even use numbers to describe how likely it is that something will happen. This measure is called a probability.

We use a scale from 0 to 1 to describe the probability that something will happen.

If something ALWAYS happens, it has a probability of ONE. For example, time continues to move forward. We are certain that this is the case, so we can say the probability of time continuing is 1.

• Can you think of anything that you are CERTAIN will ALWAYS happen?
  
• What is the probability of things that always happen?

If something NEVER happens, it has a probability of ZERO. For example, no one can jump over a big building (at least not without a rocket, or spring or something). Because we are certain of this, we can say the probability of someone jumping over a building without help is 0.

• Can you think of anything that you are CERTAIN will NEVER happen?
  
• What is the probability of things that can never happen?