what is the difference between class intervals and class boundaries while finding median, mode etc

Hello, this question has been bugging me, let's say for example i get a question in grouped data in continues variable and i have to find median but the question has giving me class limits but not class boundries. So why do i have to fins class boundries first? Please explain why class boundries is used to make midpoints or determining the size between upper and lower class of a boundry...