Using a Risp: What Can Go Wrong...

4. "The algebra is getting horrible here..."

The textbook exercises that our students have grown up on
are generally 'fixed' so that the numbers 'work out nicely'.
This is not quite what happens in real life with mathematics,
but it does have the advantage that students can concentrate on the skill they are meant to be learning
without grappling with expressions that do not factorise or with surds that refuse to simplify happily.

However, when we ask our students to take on a risp, there are no such guarantees of numerical serendipity.
They may well be choosing their own starting numbers, and given the openness of the problem, they may head off in all sorts of unexpected directions.
A risp may have a simple solution with judicious early choices, but if students bark up Tree B rather than Tree A (the one that seems obvious to us),
they may give themselves an algebraic headache. Risp 25 is a case in point:

So what is the answer? I would say that the onus is on the risp-writer to ensure that the weaker students in particular
are given a carefully-structured opening to the risp that ensures a fairly safe passage through the initial moments.
Maybe the choice of numbers or functions will have to be restricted at the start.
In other words, effective early scaffolding needs to be in place.