Probability, the first element in the reliability definition, is usually stated as a fraction or a

percentage signifying the number of times that an event occurs $($successes$),$ divided by the

total number of trials.

Satisfactory performance, the second element in the reliability definition, indicates that

specific criteria must be established that describe what is considered to be satisfactory

system operation.

The third element, time, is one of the most important, since it represents a measure against

which the degree of system performance can be related.

The specified operating conditions under which a system or product is expected to function

constitute the fourth significant element of the basic reliability definition.

Using the above information what is the meaning of each, what is the different in terms of operation

in a school to determine the number of student who passed out of $50$ students and include example

using the same school scenario.