I confess I am sometimes a little uncertain about this topic. For example, the equation x^3 - x = 20, find x to 1dp x=2.8 gives 19.152 x=2.9 gives 21.489 From here it seems likely the answer is 2.8 (My first question: how safe is it to suggest use of linear interpolation and say that 19.152 is nearer 20 than 21.489?) However, markschemes say at least one trial to 2dp should be shown. x=2.85 gives 20.299 Many students would say, I was told to show one trial to 2dp, I have done it and it gives the closest answer so I shall choose 2.85 as my answer, which to 1dp is 2.9. This leads to my second question: should you say not to try 2.85 but to use 2.84 (and 2.86 if necessary) instead and see which of those is closer to avoid the problem of 2.85 seeming to be good and leading you to give the solution as 2.9? x=2.84 gives 20.066, which is closer than 20.299, so the solution to 1dp is 2.8. How do you approach this?