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<p>A gazillion years ago, when I went to school, we didn’t have calculators. In whatever grade one learned division then, I was sent to the principal’s office for cheating on a math test. I couldn’t seem to explain why I thought it was silly to divide by 25 when you could multiply by 4, but afterwards my father advised me to just suck it up and show the division work. Okay, but I still know most of the useful reciprocals and use them all the time.</p>