There are 3 different ideas to cover studying percentages for the Junior Cert:
First of all, one of the most helpful things you can do is learn how to use the percent button on your calculator:
Finding a Percent Of…
This one is simple.
Say you are asked to find 71% of 900. Seems difficult, right? Well, all you have to do is use multiplication.
There are two ways of doing this:
- Just put 71 as a fraction over 100 and multiply that by 900, or
- Multiply 900 by 0.71.
Either method will work.
Here is the method in action:
71% of 900 is 0.71 x 900 = 639
Write as a Percent
This one is even easier!
Say you want to write 20 out of 50 as a percent. All you need to do is put 20 over 50 as a fraction and multiply by 100.
Lets also watch this in action:
20/50 x 100 = 40
Given a Percent, Find a Percent
This one is definitely the most difficult out of the three, but it can be pretty simple if we break it down. Let’s do this with an example:
If 40% of a number is 80, lets find 90%.
- What we do first is find 1%. We know that 40% is 80, so to find 1% we divide both by 40 (as 40 divided by 40 equals 1), giving us 2 as 1%.
- Then to get 90%, we multiply 1% by 90. So that’s what we do to 2 as it is 1%.
- We multiply 2 by 90, giving us 180 as our answer.
We can use other common factors as well, such as (in this instance) 10, but the above method is probably the one you will find yourself using most, as it will work in all scenarios.
Summary
And there you have it! Those are the three ways to calculate percentages for the Junior Cert. Lets go over the main points one last time:
- When finding a percent, multiply the percent over 100 by the given number.
- When writing as a percent, put the numbers into a fraction and multiply by 100
- When asked to find a percent after being given one, divide the percent and number down to 1% or another common factor, and then multiply to the percent you want to find.