Sample calculation

#1
I have a population of 2000 companies, from them, I'm sending the survey to 400 of the comapnies (a significant sample from the entire population of 2000), how many answers do I need so it would be significant sample of respondents (from the 400)?
 

hlsmith

Less is more. Stay pure. Stay poor.
#2
How are you selecting the 400? Why do you say it is a significant sample? Your use of 'significant' is confusing and undefined.