Ratio, proportion and rates of change — Edexcel GCSE Mathematics
In summary: Ratio, proportion and rates of change is a key topic in Edexcel GCSE Mathematics. Key exam tip: Always check that units are consistent before starting a calculation involving compound measures
Exam Tips for Ratio, proportion and rates of change
- Always check that units are consistent before starting a calculation involving compound measures
- Use the 'unitary method' for ratio problems if you are unsure how to proceed
- For percentage change, use the multiplier method (e.g., 1.05 for 5% increase) to save time and reduce errors
- When dealing with inverse proportion, remember that the product of the two variables is constant
- Clearly label axes and units when drawing or interpreting graphs for rates of change
Common Mistakes
- Confusing part:part and part:whole ratios
- Incorrectly applying percentage multipliers (e.g., using 0.1 instead of 1.1 for a 10% increase)
- Failing to convert units before performing calculations with compound measures
- Assuming correlation implies causation in graphical interpretations
- Misinterpreting inverse proportion as direct proportion
Marking Points
- Correct use of ratio notation and reduction to simplest form
- Accurate division of quantities into given ratios
- Correct application of percentage change, including increase/decrease and original value problems
- Correct use of compound units such as speed, density, and pressure
- Accurate interpretation of direct and inverse proportion equations
- Correct calculation of growth and decay, including compound interest
- Accurate interpretation of gradients as rates of change on graphs
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