Answer:
240 students
Step-by-step explanation:
20% of the students like rock and 40% like hip-hop. That means that 60% of the 360 students would be expected to choose one of the two. Because you don't know the other 10%, you would assume that they would have the same ratio of students who like country to those who like rock and hip-hop. 60 is 2/3 of 90 so you would expect 2/3 of the students to like hip-hop or rock. 2/3 of 360 is 240. (180 would be 50%, but you were close!)
