The value \(e\) is directly proportional to \(p\). When \(e = 20\), \(p = 10\). Find an equation relating \(e\) and \(p\). \(e \propto p\) \(e = kp\) \(20 = 10k\) so ...

There is a direct proportion between two values when one is a multiple of the other. For example, \(1\text{cm} = 10\text{mm}.\) To convert \(\text{cm}\) to \(\text{mm}\), the multiplier is always 10.