Zevachim 38A

התם חד קרא ⁠– כוליה לגופיה, וחד ⁠– לסככה; אתאי הלכתא, וגרעתה לשלישית ואוקימתה אטפח.

The Talmud answers: There, one of the 5 indicated by the verse is needed entirely for the mitzva itself, i.e., to teach the basic halakha that one must reside in a sukka. And another one of the 5 is needed to teach that a sukka, as is indicated by its name, must have a covering [sekhakha]. Accordingly, there are 3 left, alluding to the requirement that a sukka must have 3 walls. The Talmud adds that the halakha transmitted to Moses from Sinai comes and reduces the size of the third wall, teaching that it need not be complete, and sets its minimum length at only one handbreadth.

אלא מעתה, ״וטמאה שבעים״⁠ – ״שבעים״; אהני קרא ואהני מסורת ⁠– ארבעים ותרין בעיא למיתב!

The Talmud raises yet another objection: If that is so, that both the vocalized and the consonantal texts are taken into account, consider the case of a woman who gives birth to a female child. Concerning this woman the verse states: “But if she bear a female child, then she should be impure two weeks [shevu’ayim], as in her menstruation” (Leviticus 12:5). The way that the word is written allows it to be read as shivim, 70. Why not say that the vocalized text of the Torah is effective, teaching us that the woman is ritually impure for 14 days, and the consonantal text is also effective, teaching us that she is impure for 70 days, and, therefore, she should be required to sit in a state of ritual impurity for 42 days, which is the halfway point between 84 days?