GCSE Maths answers are not overly complex. Answers are usually whole numbers, so if you end up with an answer with a lengthy line of decimals, you have probably miscalculated. Go through your answer again to check your calculations are correct. If there is a decimal in the answer, it tends to be 0.5, rather than a lengthy train of decimals. If a question offers guidance as to how long you should spend on it (15 or 30 minutes, for instance), try to stick roughly within these parameters. Going well over the time guidelines for an individual question may jeopardize your chances of completing the entire exam.
Don't cross out any writing you did to work out your answers. Each question in a GCSE Maths exam is usually worth two marks or more. Even if your final answer is wrong, you may pick up a mark by clearly showing how you worked out the answer through the use of formulas or processes. If you followed the correct process but made a simple error in coming up with the answer, the examiner will see you have a degree of knowledge of the mathematical processes involved.
Inverse questions are backward equations, where the answer already is provided and you are asked to calculate the initial values and the equations undertaken before the sum was reached. As with all Maths GCSE questions, if the sums you work out involve long trains of decimals, recheck your working again as the numbers should be whole numbers. When working out mean averages, use your common sense and make sure the answer given is not above or below the highest and lowest values.
For questions involving the use of Pythagoros' theorem and trigonometry, your answers should not contain complex numbers and should not be figures higher than the length of the hypotenuse. With algebra questions, if the instructions ask you to simplify an equation, don't give a solution. Just simplify the equation into simpler components.
Probabilities are always amounts between 0 and 1 and should only be written as fractions, percentages or decimals. If your answer is outside these boundaries, go over your calculations again. For example, a question states there are 10 girls and 20 boys in a class and asks if one leaves, what the probability is that it will be a boy. An incorrect answer would be 20 out of 30, whereas giving the probability as the fraction 2/3 or a decimal of 0.66 recurring is correct.