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I’m not sure how judgmental this is meant to be (between “I thought it was kind of ironic” to “how did they ever become teachers”), but, speaking to anyone, if you think less of someone for not coming up with an answer to a simple problem as quickly as you can, I hope you realize some day how petty and self-important you’re being.</p>
<p>There are many reasons why someone who is capable of understanding a problem needs a bit more time to realize the solution. Maybe he’s sleep deprived. Maybe he was on a train of thought that just got interrupted. Maybe he has the answer automatically but is hesitant because of uncertainty. Maybe he doesn’t know as many shortcuts in mental arithmetic because calculators make them unnecessary. If you jump to the conclusion that he’s just bad at math, that’s a good indicator that you’re trying to compete with people and you want a leg up on someone to feel better about yourself.</p>
<p>Go to a culture where children regularly use an abacus to learn mental arithmetic. Compete with them; then we’ll see who is ditzy.</p>
<p>Also, I’m not sure if “to forget math” is meant to go along with poor mental arithmetic. If it is, then you’re buying right into the common misconception of what mathematics is, automatically showing that you’re worse at mathematics than someone who understands why you’re wrong. Mental algorithms are secondary to the logic from which they are derived. I would rather understand the nature of the algebraic structures that form arithmetic and how they compare and contrast with other algebraic structures than be able to subtract numbers when I don’t have a calculator.</p>