Direct and Inverse Proportion

Compare proportional relationships, find the constant of proportionality and use it to calculate missing values.

Curriculum rangeYears 9–11

y is directly proportional to x: as x gets bigger, y gets bigger by the same factor.

Constant (k)

$y = 3x$

$y = 12$

x	1	2	3	4	6	8
y	$3$	$6$	$9$	$12$	$18$	$24$

Double x and y doubles too. The graph is a straight line through the origin with gradient 3.