I think this is where a lot of people struggle.  I can look at some figures and have a rough idea what the result should be, often that is all I need. If I need an exact answer I will work it out properly.  Many of the people I work with can&#x27;t do that - note I&#x27;m not in the IT industry any more where I think mental maths was more common.<p>One example is I regularly get a spreadsheet with product and packaging weighs which we process for levy payments.  It could be the weights of the carton, EPS padding, plastic bag sleeves for kettles; all the bits you throw away.  My assistant didn&#x27;t see a problem with a tiny plastic bag weighing 4Kgs, it should have been 4g.  That was instantly obvious to me but clearly not to the supplier or my assistant.  This is the ability to estimate and get a feel for the figures and although I find it frustrating I accept that many people have a big problem with thinking like that.