GCSE · Direct & inverse proportion

Direct proportionExam-style questions

Why "directly proportional" means multiplied by a fixed number, how the unitary method and the formula y = kx are the same idea, and how to spot when a relationship is (and isn't) direct proportion.

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13 questions · GCSE (Higher) level · mark scheme and worked solution on each · no sign-up to try

DifficultyAll Level 1 Level 2 Level 3 Level 4 Level 5

1
A recipe for $12$ biscuits needs $150$ g of flour and $100$ g of butter.

Priya has $400$ g of flour and $250$ g of butter.

Work out the greatest number of biscuits Priya can make. You must show your working. [3]
Level 3 · 3 marksTry it
2
12 identical bricks weigh 30 kg. Work out the weight of 20 of these bricks.
Level 3 · 3 marksTry it
3
$y$ is directly proportional to $x$ . When $x = 8$ , $y = 36$ .

(a) Find a formula for $y$ in terms of $x$ .

(b) Work out the value of $y$ when $x = 14$ .
Level 3 · 3 marksTry it
4
$y$ is directly proportional to $x$ . When $x = 6$ , $y = 21$ .

(a) Find a formula for $y$ in terms of $x$ .

(b) Work out the value of $y$ when $x = 10$ .

(c) Work out the value of $x$ when $y = 56$ .
Level 3 · 4 marksTry it