A kid's guide to math

What are
the chances?
An intro to probability.

Every time you flip a coin, roll a die, or pick a card, you're doing math without even knowing it. Probability is the math of figuring out how likely something is to happen — and once you learn it, you'll see it everywhere.

01 The big idea

Probability tells us how likely something is to happen.

Some things are super likely. The sun coming up tomorrow? Pretty much guaranteed. Some things are super unlikely. Finding a unicorn in your backyard? Don't hold your breath. Most things sit somewhere in the middle.

The probability scale
0Impossible
¼Unlikely
½Even chance
¾Likely
1Certain
0 — Impossible
No way!
Rolling a 7 on a regular six-sided die.
½ — Even chance
50/50
Flipping a coin and getting heads.
1 — Certain
For sure
If you have only red marbles in a bag, you'll pick a red one.
02 How to find it

You can write probability as a fraction.

Don't worry — it's a friendly fraction. The top number is what you want to happen. The bottom number is everything that could happen. That's it.

Number of ways your thing can happen
— want —
— could —
Total number of things that could happen

Here's a quick example. Imagine a bag with 1 red marble and 3 blue marbles. There are 4 marbles total. The probability of picking the red one is 1 out of 4, or ¼. The probability of picking a blue one is 3 out of 4, or ¾.

03 Let's roll

A classic example: rolling a die.

A regular die has 6 sides, with the numbers 1 through 6. Each side has the same chance of landing face-up. So the bottom of our fraction is always 6.

"What's the probability of rolling a 4?"
There's only one side with a 4 on it (the orange one above), and 6 sides total. So the answer is 1 / 6. Not super likely, but not impossible either.
"What about rolling an even number?"
Even numbers on a die are 2, 4, and 6 — that's 3 sides. So the probability is 3 / 6, which is the same as 1 / 2. A 50/50 shot!
04 Heads or tails

Flipping a coin is the most famous example.

HEADS
TAILS

A coin has 2 sides: heads and tails. Each side has the same chance of landing up. So the probability of heads is 1 out of 2, or ½.

Here's something tricky to remember though: even if you flip heads five times in a row, the next flip is still ½. The coin doesn't remember what happened before. Every flip is its own brand-new question.

05 Your turn

Spin this spinner and see what happens.

This spinner has 4 equal sections — green, blue, orange, and purple. The probability of landing on any one color is 1 out of 4, or ¼. Try spinning a bunch of times — do the results even out?

Tap the button to give it a spin!

Green
0
Blue
0
Orange
0
Purple
0
06 Words to know

Some fancy words for the same ideas.

Outcome
One thing that could happen. Rolling a 4 is one outcome.
Event
The thing you're hoping for, like "rolling an even number."
Likely
Probably going to happen. More than half the time.
Unlikely
Probably not going to happen. Less than half the time.
Certain
100% going to happen, no doubt about it.
Impossible
No way it'll happen. The probability is zero.