Do not forget to take a ruler and calculator into the exam.
Maths questions often start with the command words like 'calculate', 'determine', 'estimate' and 'measure'. They will then include a blank space for you to show your working.
When an answer to a maths question is marked:
Errors carried forward are related to what happens if a later answer depends on an earlier answer, and you get the earlier one wrong. You could still get full marks in the later answer if your working is correct but you use the incorrect earlier answer.
If your answer has many decimal places or figures, make sure you give it to an appropriate number of decimal places or significant figures. You may be asked to give units. This may earn you an additional mark, so do not forget to check whether you need to do this.
Some maths questions might ask you to plot or complete a graph or table. When you draw a graph, make sure you:
You may be given a grid with axes and scales already given. Sometimes you may be given an empty grid for you to supply your own axes. When you do this:
Questions courtesy of Eduqas.
a) Complete the following sentence. [1 mark]
Half-life is the time taken for ______ to halve.
b) The table below shows how the count rate in counts per minute (cpm) changes with time for a sample of a radioactive substance.
i) Use the data in the table to plot a graph. Show the count rate on the y-axis and the time on the x-axis. Draw a smooth curve. [3 marks]
ii) Use your graph to find the count rate after 4 days. [1 mark]
iii) State the half-life of the radioactive substance. [1 mark]
a) The mass/number of un-decayed particles/count rate/cpm/activity/number of nuclei/number of atoms . Any of these would fit.
b) i) All points, smooth exponential curve. 
ii) 110 cpm 
iii) 8 days 
Iodine-131 is present in fission products of uranium. It is a beta (β) emitter with a half-life of 8 days. When absorbed into the body it concentrates in the thyroid gland, increasing the risk of thyroid cancer. After the nuclear disaster in Japan, people living in the area were given nonradioactive iodine-127 supplement tablets to reduce their intake of iodine-131 that leaked from the reactor.
The atomic number for iodine is 53.
a) i) What is a beta (β) particle? [1 mark]
ii) Explain why iodine-131 increases the risk of thyroid cancer. [2 marks]
iii) Compare the nuclear structure of I-131 and I-127. [3 marks]
b) Calculate how long people had to take the iodine supplement tablets for until the activity of iodine-131 reduced to approximately 3% of its original value just after a leak. [2 marks]
a) i) High energy, fast moving electron. 
ii) Beta absorbed/can't get out of the body  so damages/ionises cells .
iii) Both nuclei contain the same number of (53) protons  but have different numbers of neutrons.  There are 78 neutrons in I-131 & 74 in I-127 - a difference of 4 neutrons .
b) After 1 half-life it has gone down to 50%, 8 days.
2 half-lives 25%
3 half-lives 12.5%
4 half-lives 6.25%
5 half-lives 3.125%  so multiply 8 days by 5 to get an answer of 40 days .