When to use mean vs. median
The mean is what most people think of as "the average" — every value pulls its weight equally. That makes it useful for things like exam scores or measurements where values cluster fairly evenly. But a handful of extreme values can drag the mean far from what's typical: average income in a small group jumps sharply if one person earns far more than everyone else.
The median sidesteps that problem by simply picking the middle value, so it's a better summary when your data has outliers — home prices in a neighborhood, for example, or salaries across a whole company. As a rule of thumb: if the mean and median are close together, your data is fairly evenly spread; if they're far apart, something in the list is pulling the mean away from what's typical.