Blog

You will need

What’s happening?

This trick might look like magic. But it’s actually a maths trick! It’s also an introduction to the way that computers count.

There’s more than one way to write numbers. The normal way that we use is called decimal. Computers use a different way of writing numbers, called binary. Binary only has two digits: 1 and 0. In a computer, these two digits can correspond to ‘on’ and ‘off’ for electrical switches.

Binary numbers can do everything that regular, decimal numbers can do, but there are some differences. Since there are only two digits in binary, numbers have to be a lot longer. For example, 78 in decimal is written as 1001110 in binary.

Reading binary

Decimal is based around the number ten. As a result, we have a ones column, a tens column, a hundreds column and so on. Each column is ten times the value of the previous column.

Binary is based around the number two. It has a ones column, a twos column, a fours column, an eights column and so on. Each column is double the value of the previous column.

For example, the number 1001 has a 1 in the ones column and a 1 in the eights column. Its value is therefore one plus eight, or nine.

Each of the cards in this trick is focused on one digit of a number’s binary expression. If someone hands you the one and eight cards, then you know their number in binary has 1s in the ones and eights column, and 0s everywhere else. To work out the value of their number, you just have to add them up!

More information