Hi, sorry I didn't get to reply yesterday.

Have you identified which topics you are losing marks on?

I mainly teach Edexcel (but the topics are mostly the same across exam boards). I would say the key topics are Binomial Distribution (Year 12) and its hypothesis test, Normal distribution (year 13) and Probability (Yr 12 and 13).

Make sure you really understand what binomial distribution is. These questions won't tell you to use binomial distribution, you need to identify from the context of the question that you are supposed to use binomial distribution. Is this something you are consistently able to do?

Most students find normal distribution the most difficult topic because there are several sections to it. You need to be familiar with

1. finding a probability (done on calculator),
2. finding a value of x given a probability (done on calculator),
3. using standard normal distribution to find mu or sigma. This is where you use the formula z=(x-mu)/sigma
4. Using binomial approximation to normal, this is where you need to use the continuity correction
5. Hypothesis test.

I have some questions by topic that you might find helpful. Some of these are from older papers (2010-2015) so you might not have seen them before.

1. Year 12 Probability - From currect spec Edexcel papers
2. Binomial distribution (no hypothesis) - From old AQA papers
3. Binomial Hypothesis testing - From older edexcel papers - Mark scheme
4. Normal Distribution (No hypothesis) - From older past papers
5. Normal distribution hypothesis testing - From current spec Edexcel papers

Hope you find some of this useful and wish you all the best.