In a survey of students , every student studies at least one of the three subjects Maths English and Science . The number of students who study only one subject is twice the number of students who study only two students . If 20 students study all three and 80 students who study only two subjects, find the total number of students in the survey. ​

David is spreading mulch on a triangular area of his flower bed. the coordinates of the vertices of the area are (1, 3), (9, 3), and (4, 6). what is the area of the triangle if each square has an area of 3 square feet?

Suppose that 3% of all athletes are using the endurance-enhancing hormone epo (you should be able to simply compute the percentage of all athletes that are not using epo). for our purposes, a “positive” test result is one that indicates presence of epo in an athlete’s bloodstream. the probability of a positive result, given the presence of epo is .99. the probability of a negative result, when epo is not present, is .90. what is the probability that a randomly selected athlete tests positive for epo? 0.0297

How do i i solve this equation? -18 = x/3 + 3