When we add two numbers, such as $89+35$89+35, we use place value to help us and our answer would be $124$124. With decimals, we do exactly the same thing. If we were adding $8.9+3.5$8.9+3.5, we could use a place value table to help us. It would look like this, for our example:
Tens | Units | . | Tenths |
---|---|---|---|
8^{1} | . | 9 | |
3 | . | 5 | |
1 | 2 | . | 4 |
In the first video, we work through an example like this. We start in the column to the right, as we do for whole numbers, and then work to the left. Just like whole number regrouping, we can regroup when we add decimals.
Be sure to line up your numbers, so that the decimal points are in line, as this helps make sure your have the correct place value and add the numbers together correctly.
If we need to plot our answer on a number line, there are a couple of ways we could approach this. Sometimes, we can start with one of the numbers in our number problem, and move along the number line, to reflect the other number. Other times, we need to add our numbers first, and then plot them.
Have a look at Video 2, to see how we can solve our problem either way.
Adding decimals uses the same process as we use for whole numbers, but we need to consider the value of the digits and where our decimal point needs to sit.
Plot the answer to $9.8+7.9$9.8+7.9 on the number line.
Plot the answer to $3.7+0.2$3.7+0.2 on the number line.
Understand addition and subtraction of fractions, decimals, and integers