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## Put Down That Calculator

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**You don’t need a calculator to do simple
math! Learn a few tricks, and with a little practice, you’ll be
surprised how much arithmetic you can do in your head.**

Most people need a calculator to do even simple arithmetic. There’s nothing wrong with that, but if a calculator isn’t available, it can become a problem. And even if you don’t count the time to find the calculator, mental arithmetic can actually be faster than a calculator, too.

Entire books have been written on mental arithmetic, so we’re not going to cover everything in this hack. This hack covers some typical techniques useful in their own right, and some of the other hacks in this chapter are also useful in doing mental mathematics. If you find this hack interesting and useful, you can check out one of the many books on the subject, some of which are listed at the end of this hack.