How_To_Be_Good_At_Math

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

296_297_Probability.indd 297 29/02/2016 18:07