Decimals
NZ Level 5
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Add large numbers with decimal values in thousdanths
Lesson

Whole number approach

When we add whole numbers, place value is important, and we might solve a problem like $456+349$456+349, to get $805$805

This first video briefly reminds you how to add two whole numbers (with regrouping) with three digits, but you can also look at this topic on adding and subtracting 3 digit numbers to remind you how to do this.

With decimals now

We then work through an example of adding two numbers with 3 decimal places.  This means we may have numbers like $542.234+492.444$542.234+492.444, and the video takes you through how to solve this.

In the second video, you can see an example of adding two numbers with decimals, but this time we need to regroup, or rename, some decimals.  We use the same process that we use for whole numbers, so your prior knowledge, as well as the first video, will help here.

Adding decimals, with no place-value table

Finally, in our third video, we work through an example without the place value table!    Hopefully, you have seen how it helps, and now feel confident to try this yourself.  It's the same process, but we need to be careful with how we write our answers so that our numbers line up in the correct places.  

Oh, and we will also look at how to regroup from decimals to whole numbers.  You'll soon see it's the same process we always use, we just have to keep moving left.

 

Worked Examples

question 1

Evaluate $801.181+178.304$801.181+178.304

question 2

Evaluate $904.909+666.182$904.909+666.182

question 3

Evaluate $167.158+484.422$167.158+484.422. Give your answer in its simplest form.

Outcomes

NA5-3

Understand operations on fractions, decimals, percentages, and integers

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