8. A refrigeration company has six plants located in different parts of a city. Every Year, it is necessary for each plant to be completely overhauled. The overhauling is carried out in two stages A and B, and each stage requires a crew of workmen with completely different skills. The work on stage B can start only when stage A has been completed. A plant has to be closed for the entire period of its overhauling The present schedule of the overhaul of the six plants is as follows:

(a) Determine the optimal sequence.

(b) If down-time of any of the six plants costs Rs 800 per day for a plant, idle time for crew A costs Rs 250 per day, and idle time for crew B costs Rs 430 per day, which of the two schedules, the present one and the one determined in (a), will be more economical? What are their respective costs?

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P6 8 2006 2553 Plant Crew A 6 6 P Time required by crew (Days)) P2 P3 PA 4 16 Crew B 4 2 10 5