Human beings have been thinking about and counting time for thousands of years. The first time-keeping machines used sand, water or the position of the Sun in the sky to mark out the passage of time. These days, we use clocks and watches for telling the time. But however we do it, our measurement of time is based on the movement of our planet Earth in relation to the Sun.

# Mathematics

## How much money is there in the world?

Money makes the world go round, as they say, and billions of people use it every day. Most of us think of money as coins and notes that we can swap or exchange for goods and services. But if we think of money as being ‘wealth’, then that would include all the things we have that are of value – like houses, businesses, savings accounts, stocks and shares, and other resources – as well as the cash (the notes and coins) in our pockets.

So, have you ever wondered how much money there is in the world? Is it even possible to count it all? And how far would it go? It’s a question that’s tricky to answer but let’s have a go and see if we can work it out…

## What’s an algorithm?

My 7-year-old has been learning about computer programming at school. The teacher has been teaching them about algorithms by getting the children to write instructions for making jam sandwiches. Most delicious!

So, what is an algorithm? And why do computers use them?

## Can you have backwards numbers?

Numbers are useful for counting and measuring things. We use them all the time, even when we’re not thinking about maths. For example, I use them every day, for telling the time, cooking, exercising and driving my car.

Normally when we count, we start at zero and count upwards in whole numbers: one, two, three, and so on… But what happens if we count down from a bigger number – do we have to stop when we get back to zero?

## How long would it take a cheetah to run around the world?

Cheetahs are big cats that live in Africa, Asia, India and the Middle East. They can run super-fast to catch their prey when they are hunting for food. But running at top-speed is very tiring, so cheetahs only do it for short periods of time.

My 6-year-old wondered, what if a cheetah *could* run at its top-speed without getting tired…? How long would it take the cat to run all the way around the world?

Let’s do the maths and find out!

## What is the biggest number?

A while ago, I was playing a number game with my daughter. We took turns to think of bigger and bigger numbers. She started with a thousand; I said a million. But what, she wanted to know, is the biggest number?

## What is a lifetime supply of melon?

The answer to this question is a fairly simple maths calculation. Since my daughter’s favourite type of melon is a canteloupe, I’ve tried to work out what a lifetime supply of canteloupe melon might be: