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Questions tagged [arithmetic]

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64 votes
17 answers

Is there a virtue to learning how to compute by hand?

I have been professionally tutoring a wide range of students (from elementary school through graduate school) for many years. Most of them are from the United States. I generally focus on helping my ...
Geoffrey's user avatar
  • 898
12 votes
6 answers

Why does the widespread erroneous definition of "irrational number" persist without being taught?

Among the mathematically ignorant one often finds a mistaken proposed definition of "irrational number", which says that it is a number whose decimal expansion does not terminate or repeat. The ...
Michael Hardy's user avatar
10 votes
7 answers

Is this primarily a "rote computational trick" for multiplication by 9?

I tried uploading a gif, but was unable to do so. What I can do, is share a link to the gif here. (SE software seems to have allowed me to share the link, but not upload it.) What it shows, ...
amWhy's user avatar
  • 2,095
8 votes
7 answers

What's the best technique to do math calculations in my head?

I wish to teach myself how to do math calculations–like $99\times 58$ or $2048+1296$ or $506+998$–inside my head. I know there already exist two methods–Abacus and Vedic Maths. I don't know of more, ...
Gaurang Tandon's user avatar