Critical Thinking 11th Edition: Premises and Conclusions

Let's spend some time sorting out the premises and conclusions in some examples.
Choose one of the statements below. Your task is to identify the premise(s) and conclusion(s) of your example and to negotiate among yourselves if you disagree. Additionally, discuss whether the argument is valid. This exercise works best if students do not all choose the first example. If one example has been well discussed, choose a different example to discuss. 
Here are the examples: 
1.Chances are I'll be carded at JJ's, because Kera, Sherry, and Bobby were all carded there, and they all look as though they're about 30. 
2.Seventy percent of all freshmen at State College come from wealthy families; therefore, probably about the same percentage of all students at State College come from wealthy families. 
3.I am sure Marietta comes from a wealthy family. She told me her parents benefited from the cut in the capital gains tax. 
4.According to Nature magazine, today's thoroughbred racehorses do not run any faster than their grandparents did. But human Olympic runners are at least 20% faster than their counterparts of 50 years ago. Most likely, racehorses have reached their physical limits but humans have not. 
5."Let me demonstrate the principle by means of logic," the teacher said, holding up a bucket. "If this bucket has a hole in it, then it will leak. But it doesn't leak. Therefore, obviously, it doesn't have a hole in it." 
6.We shouldn't take a chance on this new candidate. She's from Alamo Polytech, and the last person we hired from there was rotten. 
What are the techniques for telling a good premise from a false one?
How can we be sure that our conclusions are sound? 
Reference should be: Critical Thinking 11th Edition by Brooke Noel Moore and Richard Parker2015 McGraw-Hill Higher Education chapter 2