Final answer:
The question about the probability that a randomly selected piece of equipment is under repair cannot be answered accurately without additional data on the total number of equipment and the number currently under repair.
Step-by-step explanation:
The probability that a randomly selected piece of equipment is under repair is not provided in the provided data. However, to find such probability, one needs information about the number of total pieces of equipment and how many of them are under repair. Without the specific data or context related to equipment repairs, we cannot accurately choose between the options (A) 10%, (B) 18%, (C) 12%, or (D) 40%. For probabilities concerning other scenarios such as defective steel rods, furnace repair times, crookedly parked cars, or finding a defective computer component, specific formulas and methods from probability theory are used. For example, the geometric distribution is used to find the probability that the first particular event happens on a specific trial.