I answered the first part. I think it is correct? But I am really lost on b. I think you just plug in the r's after you get part b -- but I am not sure. Please help! I am really confused.

1. Series-parallel configuration. Assume that a system has components C1-C4 and d dz. For the overall system to work either all type c components must work, or all d components must work. a) (10) Derive the formula for system reliability psystem works) as a function of the reliability of each component. Assume all components have the same reliability r. This is a "system works if all work" series connection problem. So, we have n components which are c_1, c_2, c_3, and c_4. Or we have d_1, d_2, and d_3. The c components are in a series with each other, as well as the d components. Since the P(system works) of a series n, we get: Pfc works) = rm4 Pfd works) = r^3 Now, since all components c must work, and not necessarily d (and vice versa), the system is in parallel. Therefore, to solve the entire system, we need to calculate it like a parallel system with respect to the c and d components. This gives us the formula: Psystem works) = 1-(1-r^4)(1-r^3). b) (5) Now assume that each component has a different reliability. c) (2) Apply the formula you developed to r=0.7 d) (3) Apply the formula developed in b) to Ra(0.8,0.9,0.9,0.9) and Rs=(0.5,0.6,0.7)