Work out direct proportion instantly with clear inputs, formula shown and shareable results.
In direct proportion y = kx, so the ratio y/x is constant. Finding k from the known pair lets you compute y for any other x.
Direct proportion
y = kx, so y₂ = y₁ · x₂ / x₁
k = 2.5 per item, so 7 items cost 17.5.
The graph is a straight line through the origin, and doubling x doubles y.