1) A. Biased because the population could be uneven. Too many of one ethnicity, too many of one gender, etc.
2) I believe this one is C. because there are not enough people. You need to survey the majority of parents instead of a selected few.
3) There are 80 green marbles per 500, therefore calculate the percentage.
or 
percent. Multiply percent or 
times 25. It gives you 
.
4) This one is a probability thing too. For every 500 batteries, there are 3 that are defective, therefore,
.
5) Yet another one. Add up all the nuts and you get
. The chance of getting a cashew from these is: 
.
Therefore:
2) I believe this one is C. because there are not enough people. You need to survey the majority of parents instead of a selected few.
3) There are 80 green marbles per 500, therefore calculate the percentage.
4) This one is a probability thing too. For every 500 batteries, there are 3 that are defective, therefore,
5) Yet another one. Add up all the nuts and you get
Therefore: