Students learn to solve word problems that involve comparing integers or integer operations, such as the following. The highest elevation is 200 feet, and the lowest elevation is –400 feet. What is the difference between the highest and lowest elevations? In the given problem, the difference between the elevations is 200 – (-400), or 200 + (+400), which simplifies to 600 feet. Note that "difference" is a key word for subtraction, while "net profit", "net change", etc., are key words for addition.