Idea 9of 22Builds onPut a probability on the line
Happening and not happening make 1
If you know how likely something is, how likely is it not?
Today you'll discover
- how the line splits in two
- why the two parts add to 1
- how to find the missing part
Think firstThe probability of orange is 3/8
The probability of orange is 3/8. What is the probability of not orange?
Decide first, then press Next. Look at what is left of the line after the event.
A probability line with a pointer at 3/8 for orange. A thick bar from 0 to 3/8 is labelled orange 3/8 and a second bar from 3/8 to 1 is labelled not orange 5/8; under them, 3/8 + 5/8 = 8/8 = 1. Then the same for rain, 2/3 and 1/3. The last step shows a line for a spinner that is 5/6 orange.
See the whole ideathe big idea and the key word, in one place
The big idea
An event and its not happening always add to 1, so not happening is 1 minus the event.
The two parts
The event and its not happening fill the whole line between them.
- orange3/8
- not orange5/8
- together8/8 = 1
Easy to get wrongTurning the fraction over is not “not”. 8/3 is more than 1, and no probability can be.
Key word
- not happening
- every outcome that does not make the event; its probability is 1 minus the event's
Ready to use it?
- Find the probability of an event not happening.