Direct proportion refers to the **relationship** between **two variables** where their **ratio** is equal to a **constant value.**

**Example:**

Given that **y** is directly proportional to **x** and that x = 19 when y = 133.

**Find:**

(i) a formula connecting y and x

(ii) the value of y when x = 13

(iii) the value of x when y = 119

**Answer:**

y ∝ x

So, y = kx for a constant k.

(i) Given x = 19, when y = 133,

133 = k x 19

k = 133 ÷ 19 = 7

Therefore, the formula is **y = 7x**

(ii) When x = 13, y = 7 x 13 = **91**

(iii) When y = 119, x = 119 ÷ 7 = **17**

It's useful to have paper and a pencil in order to record your own workings.

These are not the kind of questions you can calculate mentally.

Over to you!

Some of the questions will be reviewed by your teacher before you receive a total score.