Quick question for a-level physics

So I do the 2015 Edexcel A level Physics course and maybe this comes up in other exam boards idk,

So when you see a "show that question" usually you can do it or can't. if you can't do it, do you use the answer that it says to "show" for the next question? because most of the time the show that is to 2sf but the method they use for the next question uses a more prices answer that you shouldve gotten for the show that.

I'm saying this because even if you use the "show that" answer it is sometimes magnitudes off from the answer they want in the markscheme, if you were to use the more accurate answer.

Here's a scenario, if you have tried to get to the show that and have your own answer which you know isn't right but has more sig figs, do you use the "show that" with less sig figs or your wrong answer for the next question? Which would give more marks? This is assuming your method is completely right btw.

so use the show that answer ? although that will likely give you the wrong answer too, due to lack of sigfigs?

Cause ive seen some markschemes and it might say show that this is 15N
and u get 14.7N which is right
and then for the next question it shows them using 14.7N in the next equation
and using 15N might give u a totally different answer?

This is the only thing that confuses me when it comes to exam technique.
Also My teacher always says, for your answer you should always give it to either 2sf or 3sf, however if you need it for the next question, use the full, or as much sf as you can when putting it into the equation.

What do you think? Use the 2/3 sf value or use full value for the next question.

Cheers!