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Probability Scale

11+ Maths, topic 5.1.1

Probability Scales

In maths, you can say how likely something is to happen. This is called probability. You may be asked to place an event on a probability scale.

A probability scale

A probability scale

  • A probability scale runs from ‘impossible’ to ‘certain’.
Placing events on the scale

Placing events on the scale

  • You will be asked to place certain events on the scale, depending on how likely they are to happen.
Example A

Example A

  • I will live to be 300.
  • It's impossible to live to be 300. So you would place A at the impossible end of the scale.
Example B

Example B

  • Thursday follows Wednesday.
  • Thursday always follows Wednesday. So you would place 'B' at the certain end of the scale.
Example C

Example C

I will win £500,000 tomorrow.

  • There's a very small chance you could win £500,000 tomorrow, but it's very unlikely. So you would place C very near the impossible end of the scale.
Example D

Example D

  • I will flip a coin and it will land on tails.
  • There are 2 sides to a coin - heads and tails. So there is an even chance of this happening.

Test yourself on Probability Scale

  • Where on the probability scale would you put this event?

    You roll a dice and get an even number

  • Where on the probability scale would you put this event?

    It will rain in England at least once this year

  • Where on the probability scale would you put this event?

    You will meet Leonardo DiCaprio today

  • Where on the probability scale would you put this event?

    You roll a dice and get a number less than 5

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