Mathematics for IGCSE & O level - Proportion (Section 1 - No. 1)

Which of the following represents the correct equation if *y* is directly proportional to *x*?

y = kx

x = ky

x*y=k

x/y=k

When *y* is directly proportional to *x*, then y = kx or x = ky or x/y=k where k is a constant