What is proportion?
Proportion is a way of talking about how two variables are related to each other.
Direct Proportion: as one variable goes up the other goes up by the same Factor
eg If one variable is multiplied by 3, so is the other
Inverse Proportion: as one variable goes up the other goes down by the same Factor
eg If one variable is multiplied by 3, the other is divided by 3
You should know what the graphs look like:
How do we deal with proportion questions?
1. Identify the two VARIABLES (called A and B below)
2. Choose TYPE of proportion:
- A is DIRECTLY proportional to B use formula A = kB
- A is INVERSELY proportional to B use formula A = k÷B
3. FIND k using the values given in the question
4. Write FORMULA for A in terms of B (using your value of k)
5. USE formula to find required quantity
Edexcel GCSE Maths Notes
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