Probability
Likelihood
Likelihood is about how likely something is to happen. We use special chance words to describe events, from 'no chance' all the way to 'certain'. Knowing about chance helps people make good decisions.
The chance words
We describe likelihood with five words or phrases: no chance (impossible), poor chance (unlikely), even chance (equally likely either way), good chance (likely), and certain (sure to happen). A weather forecast might say rain is 'likely' or 'unlikely' — that is likelihood in real life.
No chance and certain
An event with no chance can never happen, like a dropped cake flying upwards. A certain event will always happen, like the sun going down today. Rolling a number from 1 to 6 on a six-sided dice is certain, but rolling a 7 has no chance.
Even chance
Sometimes two outcomes are equally likely. When you flip a fair coin, heads and tails have an even chance. A spinner that is half red and half blue has an even chance of landing on red.
Comparing outcomes
To decide the likelihood of one result, compare how many outcomes match it with how many do not. A dice landing on 5 is only a poor chance, because there are five faces that are not 5 and only one that is.
Worked examples
An event with no chance
- Think: could a dropped cake ever fly upwards?
- No — things fall down when you drop them.
Answer: There is no chance of the cake flying upwards.
A certain event
- Think: does the sun go down every day?
- Yes — it happens every single day.
Answer: It is certain the sun will go down today.
An even chance
- You flip a fair coin.
- Heads and tails are equally likely.
Answer: There is an even chance of a tail.
The likelihood of a dice landing on 5
- It is possible, so it is not 'no chance'. It is not always 5, so it is not 'certain'.
- There are more faces that are not 5 (1, 2, 3, 4, 6) than faces that are 5.
Answer: There is a poor chance the dice lands on 5.
Where you see this in real life
- A weather forecast saying rain is likely, so you take an umbrella.
- A farmer deciding which crops to grow based on the chance of rain.
- Guessing whether a coin toss will be heads or tails.
- Knowing it is certain the sun will set this evening.
Key words
- Likelihood
- How likely it is that something will happen.
- Outcome
- One of the possible things that could happen.
- No chance
- The event is impossible — it cannot happen.
- Poor chance
- The event is unlikely to happen.
- Even chance
- Two outcomes that are equally likely.
- Good chance
- The event is likely to happen.
- Certain
- The event is sure to happen.