Suppose that each relay in an electrical circuit has a relia

Suppose that each relay in an electrical circuit has a reliability of 0.9 for a specified operating period of t hours. How could you configure a system of such relays to bring RS (t) up to 0.999?

How could you configure a system of such relays to bring RS (t) up to 0.999?

0.999 / 0.9 = 1.11