In: Operations Management
A production line has three machines A, B, and C, with
reliabilities of .90, .95, and .91, respectively. The machines are
arranged so that if one breaks down, the others must shut down.
Engineers are weighing two alternative designs for increasing the
line’s reliability. Plan 1 involves adding an identical backup
line, and plan 2 involves providing a backup for each
machine. In either case, three machines (A, B, and C)
would be used with reliabilities equal to the original three.
a. Compute overall system reliability under Plan
1. (Round your intermediate calculations and final answer
to 4 decimal places.)
Reliability
b. Compute overall system reliability under Plan 2.
(Round your intermediate calculations and final answer to 4
decimal places.)
Reliability
Let reliability for A = Ra = 0.90
Rb = 0.95
Rc = 0.91
If machines are arranged so that if one breaks down, the others must shut down; this means that the machines are in series.
Hence, Overall Reliability of the line Rs = Ra * Rb * Rc = 0.90 * 0.95 * 0.91 = 0.7781
Plan 1:
Back-up is added in parallel. Overall system reliability under Plan 1 = Rp1= 1 - (1 - Rs) * (1 - Rs) = 1 - (1-0.7781)*(1-0.7781) = 0.9508
Plan 2:
Reliability of A with back-up = Rpa = 1 - (1 - Ra) * (1 - Ra) = 1 - (1 - 0.90) * (1 - 0.90) = 0.9900
Reliability of B with back-up = Rpb = 1 - (1 - Rb) * (1 - Rb) = 1 - (1 - 0.95) * (1 - 0.95) = 0.9975
Reliability of C with back-up = Rpc = 1 - (1 - Rc) * (1 - Rc) = 1 - (1 - 0.91) * (1 - 0.91) = 0.9919
Overall system reliability under Plan 2 = Rp2= Rpa * Rpb * Rpc = 0.9900 * 0.9975 * 0.9919 = 0.9795
a. Overall system reliability under Plan 1 = 0.9508
b. Overall system reliability under Plan 2 = 0.9795
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