Decimals
NZ Level 5
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Add three or more decimals
Lesson

Adding three numbers together

To add three whole numbers together, we can list them in a place value table, or underneath each other, ensuring the values are lined up correctly. To add $348+457+621$348+457+621, we would make sure we line up our units (ones), tens, and hundreds columns. Once we've added our units, tens and hundreds, we have $1426$1426 as our answer. Perhaps you might like to try this problem and see if you get that answer.

 

Adding decimals

When we add three numbers, all containing decimals, we use the same approach. With decimals, we have extra columns and the important decimal place to consider. Adding decimals is a great tool to use when you want to calculate how much something might cost you.  So, if you are purchasing items for $\$2.45$$2.45, $\$5.90$$5.90 and  $\$12.00$$12.00, you can add the three numbers together by placing each number in a place value column. Fancy trying this one?  See if you get $\$20.35$$20.35 as your answer. You can use this place value table to help.

Units (Ones) . Tenths Hundredths
       
       

Remember, we have worked on adding numbers to 2 decimal places, so why not review that topic to see what we did.  You can also review the chapter on adding numbers to 3 decimal places as well, if you like.

Let's work through an example in our video, then see how we can use this to work out the cost of going to a basketball clinic. We'll even check that our answer is reasonable using estimation.

Remember!

Adding decimal numbers follows the same process as we use with whole numbers. It's just that we now also have values to the right of the decimal point.

 

Worked examples

Question 1

$4.1+1.8+0.4$4.1+1.8+0.4

 

Question 2

$31.6+12.05+6.22$31.6+12.05+6.22

Question 3

Dave buys a packet of serviettes, a box of pies and a bag of party poppers for his party.

  1. How much do the items cost in total?

Outcomes

NA5-3

Understand operations on fractions, decimals, percentages, and integers

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