One chicken for 3 people = 183 chickens.
As many as they have the time to.
I would use about 20-21 depending on size
120
That much food would feed at least 102 people.
Chickens eat bugs on the ground if they are free range. Many chickens are living off of a grain as chicken feed.
The US Department of Agriculture (USDA) does not allow poultry farmers to feed hormones to chickens, at least to those destined for food use. (see the related link)
Yes, it will not hurt them. Ducks are often kept with chickens and they share grains. Keeping the chickens on a regular diet of duck specific grains is not a good idea as the nutritional needs of the species are slightly different. You will not get your best growth and egg production from hens fed this way.
quite a few people have pet chickens including myself, i know many other people who like them..personal preference
A blue whale can feed approximately feed 50,000 people
Many people think chickens are found in barns, they can be found in barns, fields (Stray) or human populated places.
That will feed approximately 120 people.