#### Answer

Several variables can be used:
1. the number of airplanes take off everyday, discrete variable.
2. the number of airplanes land everyday, discrete variable.
3. the number of passengers board airplanes everyday, discrete variable.
4. the number of passengers get off the airplanes everyday, discrete variable.
5. the amount of fuel needed to refill airplanes everyday, continuous variable.

#### Work Step by Step

World’s Busiest Airports A study of the world’s
busiest airports was conducted by Airports Council
International. Describe three variables that one could
use to determine which airports are the busiest. What
units would one use to measure these variables? Are
these variables categorical, discrete, or continuous?