Here are three things that might happen today or tomorrow:

• The sun will rise tomorrow morning.
• You will roll a 7 on an ordinary six-sided die.
• It will rain somewhere in Ireland this week.

Which one is sure to happen? Which one can never happen? And which one sits somewhere in between?

Every chance in the world sits on one line, from 0 at the left (it can never happen) to 1 at the right (it must always happen). The middle, 0.5, is an even chance, just as likely to happen as not.

Here is how to place an event on the scale and match its chance word. Follow this worked example: you roll an even number on an ordinary six-sided die.

• Name the outcomes: the faces are 1, 2, 3, 4, 5 and 6.
• Count how many are even: 2, 4 and 6, so three out of six.
• Three out of six is half of the faces, so the event sits at 0.5 on the scale.
• The chance word that fits 0.5 is even chance.

A coin landing heads sits on the same spot as the even-number roll. Why do you think both events land at 0.5?

• A Monday follows a Sunday.
• The next car past the school is red.
• The next baby born in Ireland is a girl.
• You will grow taller this year.

Today we place four trickier events on the scale, and each one is harder to judge than the last. Say where each belongs and why:

• The next card drawn is a heart.
• A three-colour spinner lands on your colour.
• A tossed drawing pin lands point-up.
• Your stretch: choose an event whose chance sits between 0.5 and 0.7, and defend where you put it.