Function Machines for Kids: Input, Rule and Output (Grade 8 Math)

Hi, I'm Luna from DoodleBeez. Today we are learning about functions. A function is like a machine. You put a number in, the machine follows a rule, and exactly one number comes out.

Here the rule is times two, then add one. Put in three. Three times two is six, add one, and seven comes out. Put in five. Five times two is ten, add one, and eleven comes out.

We can show a function in a table. When x is one, two, three and four, y is five, eight, eleven and fourteen. Look at the pattern. Each time x goes up by one, y goes up by three.

The amount y grows by goes in front of x, so start with three x. Then check. Three times one is three, but we need five, so add two. The rule is y equals three x plus two.

Be careful. In a function, each input has exactly one output. If the input two gives four one time and six another time, the machine is not a function. One input cannot have two outputs.

Functions are everywhere. Every movie ticket costs ten dollars. The number of tickets is the input, and the total cost is the output. The rule is cost equals ten times tickets.

Now it's your turn. When x is one, two and three, y is four, six and eight. What is y when x is ten? Pause and try. The rule is y equals two x plus two. Two times ten plus two is twenty two.

Great job! Remember, a function takes an input, follows a rule, and gives one output. See how much y grows each time x goes up by one. Practice function machines in Middle School Math at doodlebeez.com. See you next time!