Copyright © University of Cambridge. All rights reserved.

## 'Poly Plug Rectangles' printed from http://nrich.maths.org/

*This activity has been inspired by Doug Williams' Poly Plug resource. You can find out more details, including how to order sets of Poly Plug, on the Mathematics Centre website. However, you do not need sets of Poly Plug to have a go at this activity - please see below and take a look at the
Teachers' Notes.*

In this activity, the computer secretly makes a rectangle using equal rows of spots on the $5$ by $5$ grid.

The aim is for you to find the rectangle by testing spots on the interactivity below.

Click on 'Start' and the computer will tell you the total number of spots its rectangle uses.

In the left-hand 'test' grid, click on a spot to see whether it is part of the computer's rectangle. If it is part of the rectangle, the spot will turn yellow. If it isn't part of the rectangle, the spot will turn blue.

Once you think you know where the computer's rectangle is, you can create it on the 'decide here' grid. Clicking 'Reveal' will show whether you are correct.

Which spot is a good one to test first? Why?

If you had to use as few test spots as possible, how would that change the way you play?

Are there some total numbers of spots that are easier than others?

We would love to hear about the strategies you use for finding the computer's rectangle.

**If you can see this message Flash may not be working in your browser**
**Please see http://nrich.maths.org/techhelp/#flash to enable it.**