Rounding

Hello, and welcome to Myriora Maths! Is thirty-seven closer to thirty, or to forty? Let's find out!

Why do we round numbers? Imagine a toy costs thirty-seven pounds. If someone asks how much it is, you might just say: about forty pounds. Rounding gives us a number that's close, and easy to think about.

Let's put thirty-seven on a number line, between thirty and forty. Thirty-seven is three jumps from forty. And seven jumps from thirty. So it's closer to forty. Thirty-seven rounds to forty.

We don't need to draw a line every time. To round to the nearest ten, look at the ones digit. If it's zero, one, two, three or four, round down. If it's five, six, seven, eight or nine, round up.

But what about thirty-five? It's exactly in the middle: five jumps each way. So we need a rule, and the rule is: five rounds up. Thirty-five rounds to forty.

Let's try one together. Round sixty-two to the nearest ten. Look at the ones digit. Say it out loud!

The ones digit is two. Two is less than five, so we round down. Sixty-two rounds to sixty. Well done if you said sixty!

Rounding to the nearest hundred works the same way. Round three hundred and forty-eight to the nearest hundred. Now look at the tens digit, the one just after the hundreds. It's four, so we round down. Three hundred and forty-eight rounds to three hundred.

So here's the rule for any rounding. Find the place you're rounding to. Look at the digit just to its right. Five or more rounds up, and four or less rounds down. Every digit after that place becomes zero. Two thousand, six hundred and seventy-one, to the nearest thousand, is three thousand.

Here's a question that catches lots of people. Round ninety-six to the nearest ten. Some people round down, and say ninety. But six is five or more, so we round up. The next ten after ninety is one hundred! Ninety-six rounds to one hundred.

Your turn! Round four hundred and fifty-three to the nearest hundred. Pick the right card. You've got fifteen seconds, or pause the video. Go!

Time's up! Look at the tens digit: five. Five or more, so we round up. Four hundred and fifty-three rounds to five hundred!

Quick review. Rounding finds a close number that's easy to use. Look at the digit just to the right of the place you're rounding to. Five or more rounds up, and four or less rounds down. See you next time!