Adding and subtracting decimals

Hello, and welcome to Myriora Maths! What is three point four five add two point eight? Adding decimals is just like column addition, with one golden rule: line up the points! Let's see why.

Every digit has its place. Tenths must be added to tenths, and hundredths to hundredths. Lining up the points lines up all the places. And an empty place can be filled with a zero: two point eight is the same as two point eight zero.

Now add from the right, just like whole numbers. Five add zero is five. Four add eight is twelve: write two, carry one. Three add two, add the one carried, is six. Bring the point straight down: six point two five!

This is how you add money. Four pounds seventy-five, add two pounds fifty, is seven pounds twenty-five.

Taking away works the same way. Five take away one point three seven. Write five as five point zero zero, so every place has a digit. Then take away, exchanging as you go: three point six three.

Let's try one together. What is one point six add two point seven? Say it out loud!

Six tenths add seven tenths is thirteen tenths: write three, carry one. One add two, add the one carried, is four. Four point three!

Here's a question that catches lots of people. What is three point four five add two point eight? Some people line up the last digits, and get three point seven three. But that adds tenths to hundredths! Line up the points, and it's six point two five.

Your turn! What is six point four take away two point seven five? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! Write six point four as six point four zero. Then take away, with the points lined up: three point six five!

Quick review. Line up the decimal points, so the places line up. Fill empty places with zeros. Add or take away from the right, just like whole numbers. And bring the point straight down! See you next time!