Flip 2 coins, P(exactly 1 head)

Step by step

The question

Question: 2 coins are flipped.

What is the probability of getting exactly 1 head?

The probability is a fraction: the outcomes we want, over all the outcomes.

P stands for probability.

1 List all outcomes

Each coin lands heads, H, or tails, T.

Here is every outcome.

Each coin has 2 ways.

2 times 2 is 4 outcomes, all just as likely.

This list of all the outcomes is called the sample space.

2 Count the ones we want

Outcomes with exactly 1 head: HT and TH.

That is 2 outcomes we want.

3 Write the fraction

2 we want, out of 4.

So the probability is 2/4.

Careful!

0, 1 or 2 heads are not equally likely.

HT and TH are two different outcomes.

4 Simplify

Both 2 and 4 can be divided by 2.

That makes it simpler.

So it is 1/2.

5 Check

Let's check with the others.

4 minus 2 is 2.

2/4 plus 2/4 is 4/4: that is 1, all of them.

So the answer is right!

Let's look back.

First: list all outcomes.

Then: count the ones we want.

Then: write the fraction.

Then: simplify.

Last: check.