18. PQR Company has been experiencing machine breakdown for sometime and now wants to hire a mechanic on a permanent basis as against the present practice of engaging a mechanic as and when a breakdown occurs. The company has a large number of machines and, on an average, two machines breakdown per day. The machine down-time is estimated to cost the company Rs 800 per day.

Two mechanics A and B, are available. A will cost the company Rs 40 per day and can on average repair three machines per day, whereas B will cost Rs 50 per day and his average service rate is four machines per day. Describing any assumptions you might make, determine which repairman should be hired so that total expected cost per day is minimised.