Proportion - Direct

In this direct proportion video lesson, we learn how two quantities increase or decrease together at a constant rate. When one quantity doubles, triples, or halves, the other changes in the same ratio. This lesson teaches how to identify direct proportion, set up equations, and solve real-life problems efficiently using this relationship.

Related Lessons:
  1. S2 Proportion – Inverse

Direct Proportion

First, we will learn what direct proportion is and how two quantities change together in a direct proportion scenario. We will also be introduced to the direct proportion symbol, learn how to convert it into an equation, and ultimately determine the algebraic proportion equation.

Direct Proportion Example 1

Given that \(y\) is directly proportional to \(x^2\) and that \(y=45\) when \(x=3\), write an equation connecting \(y\) and \(x\).

Direct Proportion Example 2

Given that \(y\) is directly proportional to the positive square root of \(x\), and \(y=6\) when \(x=4\),

  1. find the equation relating \(x\) and \(y\)
  2. find the value of \(y\) when \(x = 16\),
  3. find the value of \(x\) when \(y=15\).

Direct Proportion Example 3

The cost, $C, of delivering newspapers, is directly proportional to the distance, d kilometres. Given that C=80 and d=50, find
  1. an equation connecting C and d,
  2. the cost of delivering newspapers for a distance of 35 kilometres
  3. the distance in kilometres if the cost of delivering newspapers is $120.
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Related Lessons:

  1. S2 Proportion – Inverse

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