Chance and probability

Hello, and welcome to Myriora Maths! Will it rain tomorrow? Will you roll a six? Probability tells us how likely something is. Let's put chances on a scale from nought to one.

On the probability scale, nought means impossible: it can never happen. One means certain: it will definitely happen. A half means an even chance, like a coin landing on heads.

In between, we say unlikely, nearer nought, and likely, nearer one. The sun rising tomorrow is certain. Rolling a seven on a normal dice is impossible.

When all outcomes are equally likely, write the probability as a fraction. A dice has six faces, and one of them is a six. So the probability of rolling a six is one sixth.

A bag has three red counters and one blue counter. That's four counters. The probability of picking red is three quarters: likely! And blue is one quarter.

Let's try one together. What is the probability of a coin landing on tails? Say it out loud!

Two equally likely sides, and one is tails. So it's one half!

Here's a question that catches lots of people. A coin lands on heads three times in a row. Some people think tails is now more likely, because it's due. But the coin doesn't remember! The probability of tails is still one half.

Your turn! A bag has two green counters and three yellow. What is the probability of picking green? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! There are five counters, and two are green. So the probability is two fifths!

Quick review. Probability goes from nought, impossible, to one, certain. A half is an even chance. When outcomes are equally likely, the probability is the number of ways it can happen, over the total. And coins and dice don't remember! See you next time!