### Crossing the Bridge

Four friends must cross a bridge. How can they all cross it in just 17 minutes?

### Coins

A man has 5 coins in his pocket. Given the clues, can you work out what the coins are?

### Flow Chart

The flow chart requires two numbers, M and N. Select several values for M and try to establish what the flow chart does.

# Simple Counting Machine

### Why do this problem?

This problem offers a simple challenge using logic gates and circuits. Through experimentation with switches and settings, students will begin to see the structure of logic gates emerge without the need for any detailed formalism. They can then move on to construct circuits with more complicated behaviours.

### Possible approach

If students haven't worked with logic gates before you could start by directing them to Circuit Maker

Put the problem on to the board. Ask students to work out what the circuit board does.

Encourage experimentation with combinations of on / off switches and different settings on the logic gates. At each stage, encourage students to predict what they think will happen, and to explain what does happen.

### Key questions

Describe what you see.
What can we change?
What will happen if we change the settings?

### Possible extension

Once the concept of the gate is understood there are several follow up problems, such as Adding Machine

### Possible support

You might suggest focussing on the AND and OR gates to begin with.