Åk 6–9

2.1 For What Do We Use Functions?
You use function everyday without really thinking about it. You calculate a functions value with the help of entering numbers in a formula.  We looked at this in the beginning with the function machine.  In the function machine, we put in a number.  A formula is the machine which does the calculation on the numbers and then “spits” out the value of the function.  For every number that we put in, only one number can come out.  The number that is “spit” out is dependent on which number which is put in.  Here are a few examples of function from everyday life.

Example A:

If you have a mobile telephone, your phone bill will depend on how many minutes you use the telephone. There is a relationship between the phone bills size and the time.  The relation is called the function and the phone bill’s size is a function of the time.

Both the phone bill’s size and the time can vary and because of this we call them variables.  In this example, the phone bill’s size is the dependant variable and the time is the independent variable.  The phone bill’s size depends on how many minutes you use the phone, just as we mentioned in the beginning.

If it costs 2 kr per minute to use the telephone then the cost would be:

Foto: Fredrik Enander

Example B:

When you are buying bananas in a store, you pay a different amount depending on how much the bananas weigh.  The price is dependence on the weight.  In this example, the price is the dependence variable and the weight is the independent variable.

The price is a function of the weight.

If the price for 1 kr of bananas is 12 kr the cost would be:

Foto: Fredrik Enander