Am I right in thinking that it isn't the case that a score of, say 70% is an A, 60% is B and 50% is a C, but in actual fact that a random top 10% get A* even if the highest score in that top 10% is only 50%?
Or are the exams just so easy that even I could get an A.
the exam board allocate standardised marks to the papers and within those marks there are set ranges for each grade, so a paper might be out of 40 but have 50 uniform marks allocated to it, to the range for an A on the uniform scheme could be 45-50 but that might correspond to 30-40 on the paper itself, so basically yes you are right!
The conversion to a Uniform Mark Scheme (UMS) became necessary when exams became modular. So, for example, in science GCSE children can take (or retake) papers either in January or June over a two year (or even more) period before 'cashing in' the all the results to get their GCSE. Since it's entirely likely that some of the papers might turn out to be slightly easier than others the raw scores are converted to UMS scores which have the fixed boundaries for the grades (90%=A*, 80%=A etc).
The actual raw scores needed to get A*s etc are sometimes ridiculously low. For example, last summer's AQA science 1 papers (higher), raw marks outof45 needed for A*,A,B,C,D were:
The actual marks needed for each grade if you'd sat these papers in January or the previous summer would be slightly different, but they do all seem rather low to me.
Oh, and if you take the difference between A and A* scores and add that to the score needed to get an A*, then that result or higher is said to be 100%! (So for Chemistry in the above example, a score of 35/45 or more would be deemed to be 100% UMS)