× 10, × 100, × 1000

Hello, and welcome to Myriora Maths! People often say: to times by ten, just add a zero. It works for twenty-three. But try it with three point five. Three point five zero is still three point five! So what really happens? Let's look.

Why do we need this? Lots of things come in tens and hundreds. A sheet of stickers has ten stickers, so twenty-three sheets have two hundred and thirty. A pencil costs thirty-five pence, so a hundred pencils cost three thousand, five hundred pence. That's thirty-five pounds. Knowing how to times by ten and a hundred makes these quick.

Here's a place value chart. Twenty-three is two tens and three ones. Times by ten, and every digit moves one place to the left. Two hundreds, three tens. The empty ones place gets a zero, to hold its place. Two hundred and thirty.

But why do the digits move? Times by ten means every one becomes a ten. And every ten becomes a hundred. So each digit is worth ten times more, and that's exactly what moving one place to the left does!

Times by a hundred? Every digit moves two places. Two thousand, three hundred. Times by a thousand: three places. Twenty-three thousand.

Let's try one together. What is forty-two times a hundred? How many places do the digits move? Say your answer out loud!

Times a hundred: two places to the left. Four thousand, two hundred! Well done if you said four thousand, two hundred!

Now, three point five. Times by ten. The three moves into the tens. The five moves into the ones. Thirty-five! The digits moved. The decimal point stayed still.

Dividing by ten does the opposite. Every digit moves one place to the right. Four hundred and sixty, divided by ten, is forty-six. And four point six, divided by ten, is zero point four six.

Here's a question that catches lots of people. What is three point five, times ten? Some people just add a zero, and write three point five zero. But that's still three point five! Move the digits instead: thirty-five.

Your turn! What is zero point zero seven, times one hundred? Pick the right card. You've got fifteen seconds, or pause the video. Go!

Time's up! Times a hundred: the digits move two places to the left. The seven moves into the ones. It's seven!

Quick review. Times by ten, a hundred, or a thousand, and the digits move one, two, or three places to the left. Divide, and they move to the right. The decimal point stays still. See you next time!