Edexcel IGCSE Maths 复习笔记 2.12.1 Direct & Inverse Proportion

Edexcel IGCSE Maths 复习笔记 2.12.1 Direct & Inverse Proportion

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 = kBA 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 the required quantity

Exam Tip

Even if the question doesn’t ask for a formula (Step 4. above) it is always worth working one out and using it in all but the simplest cases.

Worked Example

转载自savemyexam

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