Five of the ten are randomly selected for subsequent testing. Let X denote the number, among the five, that failed the preliminary test. Most discrete distributions are based upon Bernoulli processes.
Experiment is repeated n times.
Repeated trials are independent. When called upon, the guidance system for a rocket operates correctly with probability 0.9. Let n denote the number of independent but identical guidance systems in the rocket. At least one guidance system needs to operate correctly to guide the rocket.