Independent Variable
Median Age
A variable that stands alone and doesn't change by other variables that you are trying to measure.
Dependent Variable
Life Expectancy
It is something that depends on factors given, it depends on the independent variable.
Example
Someone's age can be an independent variable, your dependent variable could be something like how much they eat, how much television they watch. You would know those variables would be dependent variables because they can't change your age.