# How to Find a Probability

## Finding a Probability

A probability is a measure of how likely (how *probable*) an event is to happen.

Imagine you tossed a coin. What is the probability of the coin landing **Heads** up?

## How to Find a Probability

### Question

What is the probability of getting **Heads** in a coin toss?

### Step-by-Step:

# 1

Find the number of ways getting **Heads** can happen.

There is only **1** way of getting **Heads**.

# 2

Find the total number of outcomes.

There are **2** outomes: getting **Heads** and getting **Tails**.

# 3

Divide the number of ways of getting **Heads** (1) (found in **Step 1**) by the total number of outcomes (2) (found in **Step 2**).

Probability of getting heads = 1 ÷ 2 = 0.5

### Answer:

The probability of getting **Heads** is 0.5.

Using notation, if **H** is the event of a **Heads** coming up, the probability of the event is **P(H)**.

We can also express this as a fraction (½) or a percentage (50%).

## A Formula to Find a Probability

The formula for finding a probability is shown below:

Let's use the formula in an example.

### Question

What is the probability of rolling a 6 on a die?

### Step-by-Step:

# 1

Start with the formula.

# 2

Find the *number of ways the event can happen*.

Find the number of ways getting a **1** can happen.

There is only **1** way of rolling a **1**.

# 3

Find the *total number of outcomes*.

There are **6** outomes: getting **1**, **2**, **3**, **4**, **5** and **6**.

# 4

Substitute the *number of ways the event can happen* and the *total number of outcomes* into the formula.

### Answer:

The probability of rolling a **1** is ^{1}⁄_{6}.

Using notation, if **1** is the event of rolling a **1**, the probability of the event is **P(1)**.

We can also express this as a number (0.167) or a percentage (16.7%).