Week 6: Percentage calculations and ratios

Introduction

This week, you will continue your study of percentages. After a refresh of some of last week’s ideas, you will turn your attention to carrying out calculations with percentages. A lot of the time you see percentages in everyday life, they are about something changing – money off in a sale, or how much house prices have risen. These are the sorts of calculations you’ll be doing this week. This will help you to feel confident in using these calculations in everyday situations. Finally, you’ll spend a little time learning about ratios. Again, the activities this week will provide opportunities to practise your skills and grow in confidence.

So far in this course, you’ve learnt how to calculate a percentage, and how to find a percentage of a number. In everyday life you’ll hear a lot about percentage change, such as 20% off in a sale, or house prices going up by 5%. But percentage changes may give unexpected results – start by watching this video, which shows why you need to be careful with these sorts of calculations.

Download this video clip.Video player: swim1_week_6_demo1.mp4

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Transcript

Maria Townsend

This glass contains 200mls of water. If I add 50% to it and then reduce it by 50% will I end up back where I started? If I increase the volume by 50% I have to add 100mls, giving me 300, as in this glass here. If I reduce the volume now by 50%, that only leaves me with 150mls. As we have here. So you can see we haven’t ended up back with 200mls. This week, we’ll look at this kind of thing in more detail.

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After this study week, you should be able to:

• work out a percentage increase or decrease
• work backwards to remove a percentage increase or decrease
• understand how percentages and ratios are used in everyday life
• use ratios in calculations.