Multiplying and dividing decimals

Hello, and welcome to Myriora Maths! What is zero point three times zero point two? Lots of people say zero point six. But the real answer is zero point zero six! Let's see why.

Zero point three is three tenths, and zero point two is two tenths. On a hundred square, take three tenths one way, and two tenths the other way. Where they cross, there are six tiny squares out of a hundred. Six hundredths: zero point zero six!

Here's a quick way. Ignore the points, and multiply: three times two is six. Count the digits after the points in the question: one, and one more, makes two. So the answer has two digits after the point: zero point zero six. Try two point five times zero point three. Twenty-five times three is seventy-five, with two digits after the point: zero point seven five.

Dividing a decimal by a whole number is like short division. Four point eight divided by four. Four ones divided by four is one. Eight tenths divided by four is two tenths. So the answer is one point two.

Dividing by a decimal? Make it a whole number first. Zero point six divided by zero point two. Multiply both numbers by ten: six divided by two. The answer doesn't change: three! It's like asking how many twenty-pences fit into sixty pence.

Let's try one together. What is zero point five times zero point three? Say it out loud!

Five times three is fifteen. There are two digits after the points in the question, so two in the answer: zero point one five!

Here's a question that catches lots of people. What is zero point three times zero point two? Some people say zero point six. But a part of a part is smaller! Three tenths of two tenths is six hundredths: zero point zero six.

Your turn! What is zero point four times zero point three? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! Four times three is twelve. There are two digits after the points in the question. So the answer is zero point one two!

Quick review. Ignore the points, multiply, then count the digits after the points. Multiplying two numbers smaller than one gives a smaller answer. To divide by a whole number, keep the point in line. To divide by a decimal, multiply both numbers by ten first. See you next time!