A couple of weeks ago Stuart Price (@sxpmaths) posted this question on Twitter
I hadn’t really thought about it before but it is a bit strange that we ask similar questions about the mean in Year 7 but (I at least) have never asked an A-Level student this kind of question before.
I think it’s a really nice little question, one that is harder than you expect and gives students plenty of time to practise their algebra. My workings are below; as you can see I made a few little errors that I had to correct as I went and of course I used Wolfram Alpha instead of solving the quadratic manually!
I will definitely be using this next year when I teach S1.