The real trick is nothing more than the distributive property.<p><pre><code>  (2)(16) = (2)(15 + 1)
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&quot;Mathematical properties&quot; are just hacks that become popular because they generalize. [0]<p>[0] <a href="http:&#x2F;&#x2F;slatestarcodex.com&#x2F;2014&#x2F;03&#x2F;03&#x2F;do-life-hacks-ever-reach-fixation&#x2F;" rel="nofollow">http:&#x2F;&#x2F;slatestarcodex.com&#x2F;2014&#x2F;03&#x2F;03&#x2F;do-life-hacks-ever-reac...</a>