Probability: will it happen?
๐ In short
If you toss a coin, will it land on heads or tails? We can't know for sure, but we know both sides have the same chance. Probability is the science that measures how likely something is: impossible, possible, certain.
๐คฉ Did you know?
- Rolling two dice has 36 possible results, and a total of 7 comes up most often.
- Probability began when gamblers asked the scholars Pascal and Fermat about dice games in 1654.
- If you toss a coin 100 times, you'll get heads about 50 times.
- In a class of 23 pupils, there's a better than even chance that two of them share a birthday!
๐ Find out more
๐ Impossible and certain
The Sun rising in the east tomorrow: certain. An elephant flying by itself: impossible. Rain tomorrow: possible. We place events on a line from โimpossibleโ to โcertainโ.
๐ Writing probability as a fraction
A dice has 6 faces, and only one has a 6 on it. So the probability of rolling a 6 is 1/6, about once in every six rolls. And the probability of rolling an even number is 3/6 = 1/2.
๐ก Chance has no memory
If a coin lands on heads 5 times in a row, the probability of heads on the sixth toss is still 1/2! The coin doesn't remember what happened before.
๐ฏ In our lives
The weather presenter says: โ80% chance of rainโ, so we take an umbrella. Scientists use probability in medicine, games and insurance to make smart decisions even though they can't know the future.
๐งฎ Worked examples
- Chance of a 6 on a dice = 1/6One face out of 6.
- A bag with 3 red balls and 1 blueChance of red 3/4, and blue 1/4.
๐ Key words
- Probability
- How likely something is to happen
- Impossible
- Can never happen
- Certain
- Will definitely happen
๐งช Try it at home
Roll a dice 30 times and record how often each face comes up. Did all the faces come up about the same number of times? Then roll two dice 30 times and record the total: which total came up most?
๐งฉ Test yourself
1 What is the probability of heads when we toss a coin?
2 An elephant flying by itself isโฆ
3 How many faces does an ordinary dice have?