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Alternative Issues

Today my year 13s started work on the masses of past papers I gave them as an easter present (the lucky people that they are). One of those papers was the Edexcel C3 paper from the January sitting. One of my students today asked for help on this question from said paper:

He had managed part a easy enough and had then attempted to solve part b, when he checked his answer he had a different one so he asked for assistance. In tge first instance he said “Sir, what’s the maximum of this function?” I read the question and answered “2”, which was of little help and elicited the response “that’s what it says in the markscheme too, but how did you get it?”

The direct response for this would have been, “when you put it into alternative form R is 10, as 6,8,10 is a Pythagorean triple, so the function is maximised when the bottom is 2, meaning the max value is 2.” But I didn’t want to explain it that way, as I knew he knew how to get there. I knew exactly what he had done wrong, because I was hit with a memory from January 2013. I remember three year 13s showing up at my classroom after the exam and discussing the test, I remember the discussion around this question and I remember the look on two of their faces when one said “I nearly sodded up the alternative form question, I nearly didn’t realise that because it’s in the denominator you need to minimise the function to get the maximum.”

I knew this morning that the same thing was happening, “Did you get 2/11?” I asked. Once I had an affirmative response I asked what gave a higher number, a bigger or a smaller denominator, after a short discussion the learner grasped why you needed to minimise the alternative form bit to maximise the function. I thought I’d addressed this better since the Jan 2013 scenario, but I guess I need to ensure I fully get this across in future.

This is, however, the reason past paper practice can be an imperative part of the revision process, it gives an opportunity to diagnose these misconceptions and address them before its too late.