Ratio & ProportionStudy Notes

Worked Example 1: Using the Formula

Part of Direct Proportion — GCSE Mathematics

This study notes covers Worked Example 1: Using the Formula within Direct Proportion for GCSE Mathematics. Revise Direct Proportion in Ratio & Proportion for GCSE Mathematics with 15 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 8 in this topic. Use this study notes to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 5 of 8

Practice

15 questions

Recall

12 flashcards

Worked Example 1: Using the Formula

y is directly proportional to x. When x = 4, y = 20. Find y when x = 7.

Step 1 Find the constant k

y = kx, so k = y ÷ x

k = 20 ÷ 4 = 5

Step 2 Write the formula

y = 5x

Step 3 Substitute x = 7

y = 5 × 7 = 35

Keep building this topic

Read this section alongside the surrounding pages in Direct Proportion. That gives you the full topic sequence instead of a single isolated revision point.

Method 2: The Unitary Method Worked Example 2: Unitary Method What is Direct Proportion?Key Features of Direct Proportion

Practice Questions for Direct Proportion

Which of the following correctly reads the mathematical statement y ∝ x?

A. y is inversely proportional to x
B. y is directly proportional to x
C. y equals x
D. y is greater than x

1 markfoundation

Explain what it means for y to be directly proportional to x. Your answer should refer to the equation and the graph.

2 marksstandard

Quick Recall Flashcards

What does the symbol ∝ mean?

'is proportional to' y ∝ x means 'y is proportional to x' This is equivalent to writing y = kx for some constant k.

What does the graph of y = kx look like?

A straight line passing through the origin (0, 0). The gradient of the line equals k. If the line does NOT pass through (0,0), it is NOT direct proportion.

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Method 2: The Unitary Method

Worked Example 2: Unitary Method