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Who knows thirty?

Please cite/link your sources, if possible. After about one business day, I will:

  • Upvote all interesting answers.

  • Accept the best answer.

  • Go on to the next number.

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up vote 8 down vote accepted

At 30 years one attains full strength (Avot 5:25)

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Days before a Chag, particularly Pesach, at which one should begin studying the attendant laws.

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Thanks for the inspiration to ask this: mi.yodeya.com/questions/1381/staying-up-all-night-on-shavuot – Isaac Moses May 4 '10 at 20:56

30 are the years of the Levite draft (Num. 4:3).

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Possible source for mi.yodeya.com/questions/1371/sheloshim-mi-yodeya/1377#1377 ? – Isaac Moses May 4 '10 at 20:13
  • 30 letters (three times למשפחותיכם) is the width of each line in a Torah scroll. (Shulchan Aruch, Yoreh De'ah 272:2)

  • 30 lines are used to write the Song of the Sea (Ex. 15:1-19) in a Torah scroll. (ibid. 275:4)

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30 traits with which Malchut is attained (Avot 6:6)

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It would have been nice if the beraita would list them. – Isaac Moses May 5 '10 at 15:55

"30 days in a year is considered a year"

http://www.mechon-mamre.org/b/l/l4501.htm on daf gimmel, amud beis

http://www.halakhah.com/pdf/nezikin/Makkoth.pdf on page 7

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but so is one day (R"H 2ab (?)) – Jeremy May 5 '10 at 15:06

A person who vows to be a Nazir without specifying for how long, has to remain a Nazir for 30 days. (Nazir 5a)

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30 days in a "full" month (notice a 29 day month is called "lacking" and a 30 day month is called "complete" -I'm sure there's some significance to that)

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Gematria of the name "יהודה" is 30

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