New number skills

Rounding and significant figures

Sometimes you may come across very long decimal numbers, usually on a calculator. Often many of these digits are not important and can be ignored. This is where rounding comes in. We will explore two types of rounding, rounding to decimal places, and rounding to significant figures. 

Once you've watched both videos click on the links to go to the practice worksheets.

After completing the worksheets, you can work through the following textbook problems:

• Green Gamma - page 14 - exercise 1.06

Make sure you mark your work from the back of the book and correct any errors before progressing to the next skill!

Important: It is a good idea to round any intermediate calculations (not the final answer) to 4 decimal places, and final answers to 2 decimal places. This helps reduce any errors due to rounding.

Standard and ordinary form

Very large (or very small) numbers can take up alot of space when writing. They often won't fit on a calculator screen (and sometimes not even on the page!). To get around this, we use standard form (sometimes called scientific notation) to save space and write numbers consistently.

For example, the distance from the Earth to our nearest planet Mars is 54,600,000,000 metres. This is a number in ordinary form and - as you can see - is quite long! It won't fit on a standard calculator and can be difficult to say aloud. 

One way of saying it is 54.6 billion metres. Where did the billion come from? A billion is a thousand million, or a thousand thousand thousand, which is 1,000,000,000. A quick way or writing 1 billion is 10­9. So 54,600,000,000 can be written as 54.6 x 10­9, which is standard form.

Watch these videos to figure out how to convert between standard and ordinary form then open the links for the practice worksheets.

For further practice, work through the following textbook problems:

• Green Gamma - pages 66-67 - exercise 5.01

Make sure you mark your work from the back of the book and correct any errors before progressing to the next skill!

Ratios

Think of a ratio as a recipe for making something. For example, to get the right shade of purple when painting, you need to mix a little bit more blue paint than red paint. How much more? The recipe says that for every 2 litres of red paint, you need 3 litres of blue paint. This is written as 2 : 3. Want twice as much purple paint? Just double the recipe! 4 parts red to 6 parts blue, or 4 : 6.

Ratios are often used in cooking, but can be used whenever you need a mixture of something, whether it is making a weed killer spray (1 part weed killer to 500 parts water) or you're going on a school trip (1 adult for every 10 students).

Watch the following videos about how to split numbers up into ratios then open the links for the practice worksheets. The last one is a bit of a challenge.

For further practice, work through the following textbook problems:

• Green Gamma - 53-58 - exercises 4.02-4.03 

Make sure you mark your work from the back of the book and correct any errors before progressing to the next skill!

Need more practice?

• • Rewatch the videos

  • Go back over the previous worksheets

  • Redo the MyMaths activities

  • Check out the practice questions in the textbooks

  • Ask your teacher for some help

Ready to move on?

• Head back to the main Number page and get started on the practice assessment