Due to the space limitations of a text message, please note that it is particularly important to read carefully, pay close attention to the context of the question, and use the answers as a springboard for further study.
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Q: Do vitamins have to be kosher?
A: Although the strict opinions on this issue are prevalent, the basic halacha is that if you can’t get a kosher version of a particular vitamin, as long as they are swallow-able they are OK.
Q: Our shul did not have a minyan and we each recited the silent amidah privately, then a tenth person showed up and he did not yet daven at all. Were we supposed to recite the repetition of the amidah or was it too late?
A: If the tenth person can recite the amidah in Hebrew as chazzan, then he says an abbreviated version of the prayers prior to the amidah and then recites the amidah out-loud until the end of kedusha (see details in Shulchan Aruch 69:1); otherwise, one of the other nine is permitted to serve as chazzan and recite the full repetition (Chazon Ish cited in Shoneh Halachot, ibid.).
Q: I need to hire a worker to fix a number of things in my house, and he insists on doing it on Shabbos (apparently that’s when he’s available). We won’t be home for Shabbos. Is it allowed?
A: Ideally it is preferable to avoid it (R. Moshe Feinstein) but if it will be difficult to find another worker or to find another time to do it, it is permitted since he is a contractor that is deciding to do the work on Shabbos for his own convenience.
Q: Is it true that men can’t listen to women singing live? Why?
A: Yes, although there may be some lenient circumstances, in general it is not allowed since it is considered by the Talmud to be something that causes inappropriate arousal.