There are a ton of people on this thread saying that you need an A/A* at GCSE to be able to do A level but tbh I don't think that that's true at all. I was predicted an A* at GCSE and got a high A, but I know people in my AS maths class that got low Bs and are doing really well. I think that as long as you're really committed to the subject you can do it with a B or above. You have to really really want to do it though. I was predicted a B at AS level and at the start of the year I was getting Es and Ds because I was doing the minimum amount of work I could get away with. Once I got into the swing of things though, and started actually doing extra practise at night and past papers, my grades have gone up to B/A grade. I wouldn't even say that it's my hardest subject. Don't let people saying you need a really high grade to do maths discourage you, if you're willing to put the work in then you can definitely do it.