Answer:
Teachers to Students: 1:9, 1 to 19, 1/19
Students to teachers: 19:1, 19 to 1, 19/1
(If this is wrong the answers might be different for you but this is what I got an I was right)
1. x>20 2. x≤1 3.x<4 4.x>9 5.x≥-13