Don't forget to take a ruler and scientific calculator into the exam.
Maths questions often start with the command word 'calculate'. You need to use numbers given in the question to work out the answer.
When an answer to a maths question is marked:
Make sure you give answers to a suitable number of significant figures.
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 labelled and scales already given. Sometimes you may be given an empty grid for you to supply your own axes. When you do this:
Take extra care when converting between units.
This page contains AQA material which is reproduced by permission of AQA.
In a power station 900 MJ of thermal energy were released by burning natural gas.
a) Write down the equation that links efficiency, useful input energy and useful output energy transfer. [1 mark]
b) In a power station 900 MJ of thermal energy were released by burning natural gas. Only 405 MJ was generated.
Calculate the efficiency of this energy transfer. [2 marks]
b) = 
= 0.45 
A car has an electric motor.
The electric motor has an input energy of 50,000 joules each second.
The motor transfers 35,000 joules of useful energy each second.
Calculate the efficiency of the electric motor. [2 marks]
Efficiency = 35,000 ÷ 50,000 
0.7 or 70% 
Some power stations burn wood instead of fossil fuels to generate electricity.
A coal-burning power station burns 6 million tonnes of coal per year.
Coal has an average energy value of 29.25 MJ per kg.
Wood chip from willow trees has an energy value of 13 MJ per kg.
A hectare of agricultural land can produce 9 tonnes of dry willow wood per year.
If this power station burned dry willow wood instead of coal, how much agricultural land would be needed to grow the willow? [3 marks]
1 tonne is equal to 1,000 kg.
Coal consumption per year = 29.25 × 1,000 × 6 million
= 175,500,000,000 MJ 
1 hectare of willow will produce 9 × 13 × 1000
= 117,000 MJ per year 
So, 175,500,000,000 ÷ 117,000
= 1,500,000 (hectares) needed 
Iron is a metal that has many uses.
Iron is extracted from iron ore. Part of the process involves reduction of the ore with carbon monoxide.
Iron ore contains iron oxide (Fe2O3).
Write a balanced equation for the reaction of iron oxide with carbon monoxide. [3 marks]
Fe2O3 + 3CO → 2Fe + 3CO2
One mark will be awarded for correct formulae of reactants.
One mark will be awarded for correct formulae of products.
One mark will be awarded for correct balancing.