Since the students are to be selected at random, the concept used is Combination. The combination is 20C7 which means that "combination of 20 taken 7". The numerical value of the combination is 77520. Thus, there are 77520 ways of choosing the members of the student council.
The statement that is true regarding the sides of a triangle is the last one because the top and bottom have to be identical to each other and the sides have to be identical to each other.
