How Likely Is That? Shelly Berman shelly@mathforum.org Page 1 || Page 2 || Page 3 || Page 4 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?

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