At the college dorm open house, each of the 20 dorm members brings two guests (usually their parents). How many greetings are possible if you do not count dorm members greeting their own guests?

Consider the line y = -3/-2 x +6. find the equation of the line that is perpendicular to this line and passes through the point (-9,-3). find the equation of the line that is parallel to this line and passes through the point (-9,-3).

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.

Prove sin2a + cos2a - 1 / sin2a + cos2a + 1 = 1 - tana / 1 + cota