Answer:
N n W = {1,2,3,4}
N u W = {0,1,2,3,4,}
Step-by-step explanation:
N n W = {1,2,3,4}
N u W = {0,1,2,3,4,}
n - intersection means the common elements between N and W
U - represents all elements within N and W
You have 10 numbers to choose from, and you're choosing 4 from that pool. Order of the numbers matters, because having 1234 as a PIN is not the same having it be 1324, so we're counting the number of permutations of 10 digits taken 4 at a time. So there are

possible PINs that can be made.
Answer:
1) Is more representative
Step-by-step explanation:
The problem with his selection is that maybe there are few students participating in certain sport and those students maybe do quite more excercise than the rest (or quite less). This will modify the results because the sample he selected is biased. This problem wont be solved by method 3 or 4, because he is still selecting students that may modify heavily the results with a high probability
This problem will also appear if he choose a sample by class. Maybe, in a class there are quite few students, and selecting from class will make those students appear quite more often than, lets say, a 7th grade student selected at random, therefore the selection is biased in this case as well.
If he has a list with all seventh grade students, each student is equallly likely to be selected and as a consequence, the the results wont be biased. Approach 1 is the best one.
That's just too bad. I don't the answer. I'm just doing this to get points. Good luck.
Blue squares colored equals 6/8, add that to 1/8 (the red squares), this equals 7/8 which minus 8/8 is 1/8 which is the yellow colored squares