Marks for correct answer not fully correct method?

Should you get full marks in a part of a question if you get the correct answer with the method not fully correct or by just using trial and error? I just got my latest mock result and got 31% in paper 2. I got 43% in paper 1 which is 37% overall. However in the paper 2 I lost out on 25 marks of which all my answers were correct for them 25 marks That is over 8 percent. Which would have given me 41% overall and the pass needed. Some of the questions I knew the answer and so tried to explain how I got it but didn't explain it fully right. Others like solve for x I tried trial and error and got the correct answer. So like how many seconds for something to move above 30cm with 33sin(45t)° as equation. I just said 33sin(45x1.45)=30 30=30 so 1.45 seconds. I just kept subbing in values into my calculator like 1 was too little then 2 was too much. 1.5 just over and then 1.45 for time gave 30. I was told by another teacher once you get the right answer you should get given full marks but if you get the answer wrong and no work/ completely inaccurate work is shown you get zero marks. If anyone can help it would be appreciated.

Lol Destroyer— 20/05/16