I did probability again, I have a test on it tomorrow.
Q7) I did x out of 900, not 300. That was a simple mistake, easily avoidable if I had read the question more closely.
Q12) I guessed C for this because I didn't understand the rest. After reading the Step-by-step, I understand.
Q13) Exactly like Q7. This time it said from its total, but it also said from strain X. I was confused whether the denominator should be 40 or 17, so I stuck with 40. Turns out it was going to be more specific, so at least I know that now.
Q14) Similar to Q 12.
Conclusion: I should study probability more. I would do this same study session again to see if I've improved, but I should be working on something else now. Tomorrow I'll improve my boundaries on the R+W section, it's anchoring down my R+W score.