Using a Risp: What Can Go Wrong...

**3. Risps Presentation**

One major theme in this site
is how a slight tweak in approach can bring a question to life.

Most commonly the shift from a closed question to an open question
will accomplish this.

But even open questions need to be presented in the right way.

It is that final sprinkling of parmesan and black pepper that
makes the dish that little bit more exciting and which draws one in.

Take Risp 1. The original version of this asked:

**"When is the difference between two triangle numbers prime?"**

I guess as stated this is rather a closed question.

It is also a little unwelcoming for students.

The word 'prime' has to be attached to 'difference' which is a whole five words away.

The phrase 'prime number' will be a lot more accessible to students than
the adjective 'prime' on its own.

They also need to recall the meaning of 'triangle number' at the same time
as everything else.

The question is too dense and a little off-putting.

After working through this with a couple of classes, the risp became this:

**
Pick two whole numbers between 1 and 10 inclusive, and call them a and b.**

Say that T_{n} is the nth triangle number.

Find T_{a} and T_{b}.

What is the difference between T_{a} and T_{b}?

Is this a prime number?

When is the difference between two triangle numbers a prime number?

**
When is the difference between two square numbers a prime number?
How about the difference between two cube numbers?**

The first line is now a task that any student can accomplish.

Every student experiences a feeling of partial success on this problem that
no-one can take away!

The second line leads students gently into algebra, while testing their
understanding of 'triangle number'.

The next line asks for diagrams,
which must be a good idea.

Each step is
essential and yet accessible too.

Then comes the revision of the idea of a prime number,
at which point everything is in place to make sense of the main question.

This can then be opened out in a variety of ways.

There are many times when I have come close to discarding a risp,

only to discover that a slightly different way into the question can
revitalise it.