Nisaab of Zakaat

Q: A young Mufti (scholar) said to calculate zakaat based on gold. Now he changed his ruling and says to give it based on silver. So, based on gold, the zakat was 3000$. Today when he told the people to do it based on silver, todays silver price was 500$. So what must the people do on paid zakaat, count what is paid on gold as okay and from here on pay of silver?

Reciting the Tasmiyyah at the time Slaughter

Q: I am a PhD, Electronics Engineering, student in Torino, Italy. I have a question regarding chicken meat. There is a slaughter house near our city where Arab Muslim use to slaughter chickens. He slaughters the chicken by hand. Usually he has to slaughter approximately 7,500 chickens in 6 hours. He use to say Takbeer randomly, and not on each individual chicken. He says that it is quite difficult for him to say takbeer on each chicken. We had read in one of Mufti Taqi Usmani Sahib's (db) book that according to Imam Shaafaee (Rehmat Ullah Alaih), it is sunnah to read takbeer during slaughtering. This is the only slaughter house in our knowledge where there is no machine slaughtering of chicken. Now my question is that, if person is slaughtering so many chickens, is it a MUST for him to pass takbeer on each individual. Is it possible for us to eat that chicken if that person is slaughtering correctly according to Fiqh Shafaee?

Islamic etiquettes with regards to answering the door

Q: What is the Islamic etiquette with regards to answering the door when someone knocks. Some people don't answer the door or delay for quite some time before answering the door for no reason at all. In some cases if the person is eating or reading Qur'an, etc, he doesn't answer the door or delays unnecessarily. The person doesn't even announce to the knocker informing him that he has heard him. Is this not inconveniencing the visitors? Please explain the correct conduct and etiquette.

Birthdays

Q: What is the ruling regarding birthdays? Our muslims greet one another on this day and feel insulted if one does not greet them. Another issue is regarding birthday cakes, gifts and parties. Please advise.