# Flow charts

Source: https://projectgcse.co.uk/maths/algebra/flow_charts

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Flow charts show a set of instructions which are to be followed. When you put a value into the start of the flow chart and follow the results you should get a result.

Flow charts are made up of boxes, each with their own function. The shape of the box shows what it is doing.

|  | Used to show the start or end of a sequence |
| --- | --- |
|  | Contains the instructions you follow |
|  | These are decision boxes which contain yes or no questions |

These boxes are joined together by arrows which shows the direction you have to follow the instructions.

An example of a simple flow chart follows:

![](https://content.projectgcse.co.uk/img/maths/flow1.gif)

If you think of a number and follow the flow chart you would get a new result.

If you think of the number 2, you would:

- add 5 to 2 to get 7
- multiply 7 by 3 to get 21

This means when you put 2 in, you get 21 out.

You can get the same result by using the equation y = 3 ( x + 5 ). Where x is the number you put in and y is the result. As a function, it would be seen as: f(x) = 3 ( x + 5 )

When looking at the equation you can easily change the subject:

- y = 3 ( x + 5 )
- y/3 = x + 5
- y/3 - 5 = x

This means the inverse function is: f-1(x) = x/3 - 5

This can be made into an inverse of a flow chart:

![](https://content.projectgcse.co.uk/img/maths/flow2.gif)

If you think of a number and follow the flow chart you would get a new result.

If you think of the number 21 from the first result, you would:

- divide 21 by 3 to get 7
- subtract 5 from 7 to get 2

The inverse has returned the number back to what the subject used to be.