An elevator for a building must be greater than (or equal to) floor zero and the top floor. For a 20-floor apartment building with no basement, we can represent the elevator reaching all of the floors between the ground floor and the top floor, or 0≤x≤20. In words, we can say that the elevators must be able to reach greater than or equal to the ground floor AND less than or equal to the 20th floor.
A car burns more gasoline when it’s going either really slow or really fast. When we look at how the different ways driving a car can be more expensive, a car must be going below 40 miles an hour and higher than 70 miles an hour. The inequality to represent this is the speed is less than 40 miles per hour OR greater than 70 miles per hour. We can say, x<40 or x>70.
