What most people do not know is that the weather on a mountain can change within minutes.

Imagine you are setting out to walk up the side of Snowdon, the highest mountain in Wales. It will take all day.

It is a lovely sunny day and you don't want to carry a heavy rucksack. So you think you will just take a picnic lunch and no spare clothes.

You see other people with rucksacks packed more fully than yours and you laugh at them for weighing themselves down.

Are you wise to laugh?

As a class, work out what they might have in their rucksacks.