Considering N users, with indices i = 1, 2, 3, ..., N. Suppose that we have collected the data reflecting whether user i knows j and assume everyone knows
themselves (of course).
(1) Use the concepts in linear algebra to represent the data of who knows whom? (5%)
(2) How to measure the similarity between two users from the people they know, say they
are more similar if they know more users in common?

Will give the box plots below show the math scores of students in two different classes: class a 55 72 75 89 95 class b 55 70 75 94 100 based on the box plots, which statement is correct? a: the median score of class a is greater than the median score of class b. b: the lower quartile of class a is greater than the lower quartile of class b. c: the upper quartile of class a is greater than the upper quartile of class b. d: the maximum score of class a is greater than the maximum score of class b.