I am very sorry for the myriad of probability questions but I have a dam hard time trying to understand these questions:
This is the question:
Consider the following portion of an electric circuit with three relays. Current will flow from point a to point b if there is at least one closed path when the relays are activated. The relays may malfunction and not close when activated. Suppose that the relays act independently of one another and close properly when activated, with a probability of .9.
The question is: What is the probability that current will flow when the relays are activated?
1 - (0.1)^3
I don't understand why you are multiplying 0.1 * 0.1 * 0.1 and not adding 0.1 + 0.1 + 0.1. Since if any one of the three are open then the current will flow so isn't this technically a union which means you add?