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Complements to 100

Find the pairs of numbers that add up to 100.
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This is level 3: complements true or false.

You will be awarded a trophy if you get at least 9 answers correct and you do this activity online.

1

$$40 + 60 = 100$$

☐ ☐ ✓ ✗

2

$$43 + 67 = 100$$

☐ ☐ ✓ ✗

3

$$71 + 39 = 100$$

☐ ☐ ✓ ✗

4

$$25 + 75 = 100$$

☐ ☐ ✓ ✗

5

$$75 + 25 = 100$$

☐ ☐ ✓ ✗

6

$$5 + 85 = 100$$

☐ ☐ ✓ ✗

7

$$100 = 77 + 33$$

☐ ☐ ✓ ✗

8

$$100 = 22 + 78$$

☐ ☐ ✓ ✗

9

$$100 = 61 + 39$$

☐ ☐ ✓ ✗

10

$$45 = 100 - 65$$

☐ ☐ ✓ ✗

11

$$47 = 100 - 53$$

☐ ☐ ✓ ✗

12

$$100 - 17 = 83$$

☐ ☐ ✓ ✗

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This is Complements to 100 level 3. You can also try:
Level 1 Level 2

Instructions

Try your best to answer the questions above. Type your answers into the boxes provided leaving no spaces. As you work through the exercise regularly click the "check" button. If you have any wrong answers, do your best to do corrections but if there is anything you don't understand, please ask your teacher for help.

When you have got all of the questions correct you may want to print out this page and paste it into your exercise book. If you keep your work in an ePortfolio you could take a screen shot of your answers and paste that into your Maths file.
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Complements to 100

Complements to 100

Find the pairs of numbers that add up to one hundred. So far this activity has been accessed 64 times and 5 Transum Trophies have been awarded for completing it.
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Comment recorded on the 2 May 'Starter of the Day' page by Angela Lowry, :

"I think these are great! So useful and handy, the children love them.
Could we have some on angles too please?"

Comment recorded on the 1 February 'Starter of the Day' page by M Chant, Chase Lane School Harwich:

"My year five children look forward to their daily challenge and enjoy the problems as much as I do. A great resource - thanks a million."

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Description of Levels

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Level 1 - Identifying numbers shaded in a 100 grid

Level 2 - Find the complements

Level 3 - Complements true or false

More on this topic including lesson Starters, visual aids, investigations and self-marking exercises.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

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The questions in Levels One and Two are randomly generated, so pupils will face new challenges each time they practise—even if they complete the same level every day. This regular exposure to fresh problem sets helps to build confidence and reinforce key skills. In particular, repeated practice with complements of 100 helps pupils internalise these relationships, making it easier for them to quickly recognise and use them in other mathematical contexts. By promoting daily engagement and encouraging pupils to revisit the exercises frequently, these online activities serve as a valuable tool to consolidate knowledge and support ongoing progress.

Example

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How to Mentally Find the Complement of 63

Here’s a simple way to work it out step by step in your head by looking at the ones digit first, then the tens digit:

Look at the Ones Digit:

Ask yourself, “How many do I add to 3 to make the next full ten?” 3 needs 7 to reach 10, so you add 7 to 63 to reach 70.

Look at the Tens Digit:

Now you’re at 70 (7 tens). How many more tens do you need to reach 100? From 70 to 100 is 30, which is 3 tens.

Combine the Steps:

You added 7 to get to 70, and then 30 to get from 70 to 100. Altogether, 7 + 30 = 37.

So, the complement of 63 is 37, because 63 + 37 = 100.

Don't wait until you have finished the exercise before you click on the 'Check' button. Click it often as you work through the questions to see if you are answering them correctly. You can double-click the 'Check' button to make it float at the bottom of your screen.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

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