Function Machines

A function machine is a diagram that shows an operation (or chain of operations) applied to an input. You read it left to right: the input enters, the machine applies a rule, and the output comes out the other side.

When there are two machines in a row, you feed the output of the first into the second. For example, if the input is $4$, the first machine says $\times 3$ and the second says $+ 2$, then the output is $4 \times 3 + 2 = 14$.

You can also work backwards (inverse operations). To undo $\times 3$ you $\div 3$, and to undo $+ 2$ you $- 2$.

Try different inputs and watch the value change as it flows through each machine.

Watch it work

Question: A two-step function machine does $\times 2$ then $+ 5$. Find the output when the input is $7$.

Question 2: The output of a function machine is $20$. The machine does $\times 4$ then $- 8$. What was the input?

Have a go