What Are the Chances?

Lesson Plan - Get It!

Audio:

• Was I right? Did you catch yourself laughing?

In the video, Tom Cruise said it would be “impossible” for his second egg to also be raw; but he was wrong. Perhaps he should have said that it would be “unlikely” for the second egg to be raw. Sometimes, even when something is unlikely to happen because the probability is low, it happens anyway. This is because probability is never certain. It is simply a description of how likely or unlikey something is to happen.

Before we figure out whether probability was on Tom Cruise’s side or not, let’s find out the answer to...

• What exactly is probability?

Put simply, probability is how likely something is to happen.

Many scientists and social scientists use probability, including meteorologists, who predict the weather, and epidemiologists, psychologists, economists, and statisticians. They predict outcomes of events, such as the incidence of diseases and the strength of the stock market. For them, probability is an important part of every day.

Let’s explore probability and learn what it takes to make good predictions.

Even though we wish we could know for certain that something is going to happen, we realize that most things cannot be predicted with total certainty. The best we can say is how likely they are to happen, using the concept of probability.

For example, when you toss a coin, there are only two possible outcomes or ways it could land:

• heads

• tails

So, we can say that the probability of the coin landing on heads is one in two, or ½, and the probability of the coin landing on tails is also one in two, or ½. There is only one head and one tail, so it can only happen one way.

We can apply the same idea when tossing a pair of dice. When you throw just one die, there are six possible outcomes or ways it can land: 1, 2, 3, 4, 5, or 6. So, the probability of any one of them is one in six or ¹/₆. There is only one of each number face on one die, so it can only happen one way.

We can define the formula for probability in the following way:

Tom learned a valuable lesson: Probability doesn’t tell you what will happen; it only tells you how likely it is for something to happen. Consider some of the examples of probability you have experienced in your own life!

Then, move on to the Got It! section for more probability practice.