For the exam, is there a hard and fast rule on how many decimal points or significant figures are required for the solutions? Both intermediate calculations and the final answer?
You want at least 3 SF for percentages or probabilities and I would go for at least 5 SF for other numbers (or nearest pound or nearest penny). Every calculation tends to lose a SF of accuracy - so either store the numbers in your calculator (and maybe write some of it for the examiner eg 3.456.......) or write down and retype into your calculator enough figures so the answer will be correct to the desired level of accuracy.
Is it wrong if i just leave my final answers to quite a few SF (let say 5) regardless if i might be using it for the next subsection?
Not at all. The only issue that would cause loss of marks is over rounding (and thus getting inaccurate answers) or not obeying a command in the question to give it to a certain number of places.
