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Challenge Level Yellow star
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Here are lots of small chains, each with a certain number of links.  The chains that we will use have these numbers of links:  2, 3, 4, 5, 6, 8, 9, 10 and 12. There are many of each size available.

Suppose we want to make a twenty-link chain from the sizes above, then we could use two of the ten-link small chains. Each ten would just be $\frac{1}{2}$ of the 20.
In this case we could write:
 
Half plus half makes one whole, or, $\frac{1}{2} + \frac{1}{2} = 1$  
where the twenty-link chain is the ONE (1)

What other selection of chains could you put together to make the twenty-link chain, using only the sizes that you see at the top?
Try writing the fractions down in different ways.

Find as many different ways of making a twenty-link chain as you can.

 
What happens if you try to make a twenty-four-link chain?

Here is an example using a twelve-, an eight- and a four-link chain:
 
We could write:
$\frac{1}{2} + \frac{1}{3} + \frac{1}{6} = 1$  
where the twenty-four-link chain is the ONE (1)

Or, we could write:
a half plus a third plus a sixth makes a one 

How many ways can you find to make a twenty-four-link chain?
 
 
A very different one to try is a twenty-seven-link chain, so 27 is your ONE.  Have a go!

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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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