The total area under the probability density function over the entire range of values the random variable X can possibly take is the same for all continuous random variables. What is that total area? What probability does it represent?
Suppose the random variable is the amount of rainfall in Davis, California, for a randomly selected year and can range from 0 inches to 50 inches.
What is the area under the appropriate density curve over the range from 0 to 50 inches? What probability does it represent?