Rule of seven

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A so-called rule of seven (or rule of seven ) exists in a wide variety of subject areas. As a rule, this describes a situation that is related to the number 7.

The Siebenerregel there

  • as a standing term in radiation protection . It says here that after seven half-lives the activity of a radioactive nuclide has decreased to about 1% (exactly to one 128th). The rule of seven is useful for estimating how long what activity has been going on in a contaminated area.
  • in mathematics for the divisibility of an integer by 7. For example: "A number is divisible by 7 if and only if its alternating 3-digit sum is divisible by 7."
  • for the cube . The eyes of a dice are usually arranged in such a way that the sum of the opposite numbers results in 7.