13.1 The probability scale · Unit 13 Probability

1 · Teaching slidesuse ← → keys

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2 · Key words

probabilityHow likely something is, on a scale from 0 to 1.

impossibleIt can never happen; probability 0.

certainIt must happen; probability 1.

even chanceJust as likely as not; probability 1/2.

outcomeOne possible result.

eventThe outcome or outcomes you are interested in.

probability scaleThe line from 0 to 1 that every probability sits on.

3 · Summary of the sectionrevise from this

Every probability lies between 0 and 1. Nothing is less likely than impossible or more likely than certain.
0 = impossible, 1/2 = even chance, 1 = certain.
A probability can be written as a fraction, a decimal or a percentage — all three mean the same thing.
0.2 = 1/5 = 20%. Convert to one form before comparing.
Words like “probably” mean different things to different people; a number does not.
An outcome is one possible result; an event is the outcome or outcomes you care about.
An event and its opposite have probabilities that add to 1.
A probability of 1/2 does not promise that exactly half of any set of trials will succeed.

PDFPrintable worksheet All 47 questions, space to work PDFWorked answers Full solutions, not just the answer

Video lessons2 videos

Math Antics - Basic Probability

American mathantics

What probability means and how it is written. Note the channel's own correction: “odds” and “probability” are not the same thing.

The Probability Scale

British corbettmaths

Placing events on the 0-to-1 line, and the words that go with each part of it.

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The probability scale