You'll need to be a very able student, not make any silly mistakes and have the questions go your way, i.e. topics you are particularly good at or ones you revised recently.
Well, we'll see in August. DS is very able (at maths), always makes silly mistakes and hasn't done any revision for maths, apart from what he did in class and the handful of past papers the teacher gave him as homework over the Easter holidays.
DH and I tried to get him to revise maths yesterday, but he refused point blank. He eventually offered a compromise yesterday that if today had any challenging questions, then he'd revise for paper 3. But it didn't.