How to Use Probability to Make Predictions

Kenny has a box of 5 kittens.

If Kenny reaches into the box without looking, what's the chance that he gets a white kitten?

We can't say for sure. We need to make a prediction.

      A prediction is a guess about what could happen.

We can use probabilities to make a prediction.

Finding the Probability

      Probability is the likelihood that an outcome will happen out of all the possible outcomes. 

      To find a probability, we divide the number of favorable, or desired, outcomes by the total possible outcomes.

Tip: "P" often stands for probability.

      A favorable outcome is the outcome we want to get.

Let’s make a prediction about which cat Kenny gets using probability. 😀

First, we count all the possible outcomes.

There are 5 kittens. There are 5 possible outcomes.

Next, we list the number of favorable outcomes.

We want Kenny to get a white kitten.

2 kittens are white. There are 2 favorable outcomes.

We divide the favorable outcomes by the total possible outcomes to get the probability:

The probability of getting a white kitten is 2/5. This is also equal to 4/10, or 0.4, or 40%. ✅

Example 2: Spinning a Wheel 

Sally is playing with this shape spinner game.

Let’s say she spins it 8 times. 

How many times can she expect to get a square?

To figure this out, first let's find the probability of getting a square for each spin.

There are 4 squares in the spinner. This is the number of favorable outcomes.

There are 8 total possible outcomes.

Do you remember how to find probability?

Yes! Divide the number of favorable outcomes by the total possible outcomes.

The probability of getting a square for every spin is 4/8.

Now, we multiply this probability by the number of times she spins.

How many times does she spin?

Yes, 8 times.

We can simplify 32 / 8:

32 ÷ 8 = 4

The best prediction is that she will get a square 4 out of 8 spins.

This is her called her expected value.

Fantastic job.

Now, start the practice to help you learn more.