# Science calculations

Maths questions often start with the command words 'calculate’ or 'determine'. They will then have a blank space for you to show your working. It is important that you show your working; don’t just write the answer down. You might earn marks for your working even if you get the answer incorrect.

In some maths questions you will be required to give the units. This may earn you an additional mark. Don't forget to check whether you need to do this.

Maths questions might include graphs and tables as well as calculations. Don't forget to take a ruler and calculator.

If drawing graphs, make sure you:

1. put the independent variable on the x-axis and the dependant variable on the y-axis
2. construct regular scales for the axes
3. label the axes appropriate
4. plot each point accurately
5. decide whether the origin should be used as a data point
6. draw a straight or curved line of best fit

If you are asked to calculate an answer and it has lots of decimal places, don't forget to use the same number of significant figures as the data in the question. For example, if two significant figures are used in the question, then usually your answer would also be to two significant figures. Don't forget to check your rounding.

Edexcel questions courtesy of Pearson Education Ltd.

## Sample question 1 - Foundation

Question

A student wants to estimate the number of daisy plants in a 500 m2 field.

She uses a 1 m2 quadrat to sample the field.

The figure shows the results for the number of daisy plants counted in six areas sampled with the quadrat.

157 cm
222 cm
369 cm
433 cm
545 cm
646 cm

Calculate the mean number of daisy plants for the six samples. [1 mark]

Mean number of daisy plants = 5 + 2 + 6 + 3 + 4 + 4 = 24

Divide by the number of quadrats.

=

= 4 (1 mark)

## Sample question 2 - Higher

Question

The figure shows a food chain for organisms in a stream.

Algae → Stonefly larvae → Water beetles → Birds

In the food chain there is 2.1 × 104 J of energy in the biomass of stonefly larvae.

90% of the energy is lost between each trophic level of the food chain. Calculate the energy value that enters the birds. [2 marks]

• 2.1 × 104 = 21 000 × 0.1 = 2 100 J in the water beetle (1 mark)
• 210 J in the bird (1 mark)