## Copy and complete this table without using a calculator!

 120 960 2040 7680 10% 50% 25% 33⅓% 75% 90%

## A Mathematics Lesson Starter Of The Day

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• Transum,
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• Transum's exciting, fascinating and surprising starters are balanced by this more routine practice exercise. Having said that some pupils will find it a revelation when they learn (from other pupils) tricks for quickly working out these common percentages. A really useful way to spend the first ten minutes of the lesson.
• Dylan T, Charnwood Primary Lichfield
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• This was a good starter especially if your target is percentages!
• Faye D Year 6, Charnwood Primary Lichfield
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• A good starter as it got my brain working and lots of people found it challenging.

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% - This is the percent symbol.
Percent means 'out of 100'.

### Find 50%:

As 50 is half of 100, then 50% means half. To find 50% of a quantity you need to halve (or divide by two). So 50% of 6 is 3.

### Find 10%:

As 10 is one tenth of 100, then 10% means 'one tenth of'. To find 10% of a quantity you need to divide it by ten. So 10% of 800 is 80.

### Find 25%:

As 25 is one quarter of 100, then 25% means 'one quarter of'. To find 25% of a quantity you need to divide it by four. So 25% of 20 is 5.

Another way of finding 25% of a quantity is first finding 50% then dividing the result by 2.

### Find 33⅓%:

As 33⅓ is one third of 100, then 33⅓% means 'one third of'. To find 33⅓% of a quantity you need to divide it by three. So 33⅓% of 30 is 10.

### Find 1%:

As 1 is one hundredth of 100, then 1% means 'one hundredth of'. To find 1% of a quantity you need to divide it by 100. So 1% of 800 is 8.

### Find other percentages:

Other percentages can be found by combining some of the techniques mentioned above. Here are some examples:

• To find 75% of a quantity add together 50% and 25% of it.
• To find 20% of a quantity double 10% of it.
• To find 5% of a quantity halve 10% of it.
• To find 66⅔% of a quantity double 33⅓% of it.
• To find 90% of a quantity subtract 10% from it.
• To find 80% of a quantity subtract 20% from it.
• To find 2% of a quantity double 1% of it.
• To find 52% of a quantity add 50% to 2% of it.

If you need to use a calculator to check your working. See Calculator Workout skill 3.

### Commute

Did you know that if you are struggling to mentally work out 24% of 50 you can switch the numbers round and work out 50% of 24 instead. Finding 50% is very easy isn’t it? You will get the same answer.

Finding a percentage of a quantity is an example of a commutative calculation. Not all operations are commutative. Subtraction certainly isn’t as 10 minus one is not the same as one minus ten.

You can use this trick to improve your ability to do this type of calculation quickly if you find the switch makes it easier.

Practise with 12% of 50, 4% of 25 and 75% of 10.

 120 960 2040 7680 10% 12 96 204 768 50% 60 480 1020 3840 25% 30 240 510 1920 33⅓% 40 320 680 2560 75% 90 720 1530 5760 90% 108 864 1836 6912

Note to teacher: Doing this activity once with a class helps students develop strategies. It is only when they do this activity a second time that they will have the opportunity to practise those strategies. That is when the learning is consolidated. Click the button above to regenerate another version of this starter from random numbers.

Your access to the majority of the Transum resources continues to be free but you can help support the continued growth of the website by doing your Amazon shopping using the links on this page. Below is an Amazon search box and some items chosen and recommended by Transum Mathematics to get you started.

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## A Compendium Of Mathematical Methods

How many different methods do you know to solve simultaneous equations? To multiply decimals? To find the nth term of a sequence?

A Compendium of Mathematical Methods brings together over one hundred different approaches from classrooms all over the world, giving curious mathematicians the opportunity to explore fascinating methods that they've never before encountered.

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 Teacher, do your students have access to computers?Do they have iPads or Laptops in Lessons? Whether your students each have a TabletPC, a Surface or a Mac, this activity lends itself to eLearning (Engaged Learning).

Transum.org/go/?Start=October16

Here is the URL which will take them to a related student activity.

Transum.org/go/?to=pchange

## Curriculum Reference

See the National Curriculum page for links to related online activities and resources.

For Students:

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