STATISTICS • PROBABILITY 297
It's likely that at least one
person among the pupils and
staff at your school will have a
birthday this week.
At this moment, it's very likely
that somewhere around the
world a plane is flying in the sky.
We can be certain that the sun
will rise tomorrow morning.
Sunrise scores 1 and sits at the very
top of the probability scale.
Probability scale
All probabilities can be shown on a line called a
probability scale. The scale runs from 1 to 0. An
event that’s certain is 1, something that’s impossible
is 0. Everything else is in between these values.
There is an equal chance of
getting heads or tails when
you toss a coin. Equal chance
is the scale’s halfway point.
There's little chance of you
being struck by a bolt of
lightning. Although it’s possible,
it’s very unlikely.
Flying elephants score 0 on
the scale. Elephants don’t
have wings, so it’s impossible
to see a flying elephant.
It's unlikely that if you roll two
dice you will throw a double
six. As you’ll know from board
games, it doesn’t happen often!
Anything that
scores 1 is sure
to happen
An event with a
probability of^1 / 2
is just as likely to
happen as not
Likelihood
increases
closer to 1
Likelihood
decreases
closer to 0
An event with a
probability of O
can't happen
1
0
UNLIKELY
EQUAL CHANCE
VERY UNLIKELY
IMPOSSIBLE
LIKELY
CERTAIN
VERY LIKELY
more likely
less likely
1
2
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