### Overarch 2

Bricks are 20cm long and 10cm high. How high could an arch be built without mortar on a flat horizontal surface, to overhang by 1 metre? How big an overhang is it possible to make like this?

### Stonehenge

Explain why, when moving heavy objects on rollers, the object moves twice as fast as the rollers. Try a similar experiment yourself.

### Maximum Flow

Given the graph of a supply network and the maximum capacity for flow in each section find the maximum flow across the network.

# New Units for Old

### Why do this problem ?

This important problem will lead to a thorough understanding, and demystification of, the various units which exist. Students will enage in a variety of problem solving strategies in its solution.

### Possible approach

This question initially appears to be quite demanding. Provide a printout of the data to each student. Which units are already known? Suggest that these first be crossed off, with the results tabulated elsewhere. This will significantly reduce the scale of the problem.

### Key questions

Are there any obvious pieces of data with which to start?

### Possible extension

Extension activities are given in the question. Can students find examples for each of the units?

### Possible support

Create cards for a team card sorting exercise, allowing students to move the various data around physically.

As a warm-up, you might try Choose your units.