Who knows thirty?
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Sign up to join this communityPlease 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.
Days before a Chag, particularly Pesach, at which one should begin studying the attendant laws.
30 are the years of the Levite draft (Num. 4:3).
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)
"30 days in a year is considered a year"
http://www.mechon-mamre.org/b/l/l4501.htm on daf gimmel, amud beis
A person who vows to be a Nazir without specifying for how long, has to remain a Nazir for 30 days. (Nazir 5a)
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)
As we see in מדרש תנחומא חיי שרה סימן ו, thirty out of the seventy nations were scattered during the דור הפלגה. To make up for this, thirty nations came from Avrohom: the twelve sons of Yishmo'eil, the six sons of Keturoh, the two sons of Yokshon (the second son of Keturoh), the three sons of Dedon (the second son of Yokshon), the five sons of Midyon (the fourth son of Keturoh), and the two sons of Yitzchok (Yisro'eil and Edom, obviously!), which also explains a different question.