Posted by Peter on .
The Carbon coal company has 2 mines, a surface mine ad a deep mine. it costs $200 per day to operate the surface mine and $250 to operate the deep mine. Each mine produces a medium grade and a medium-hard grade coal, but in different proportions. This surface mine produces 12 tons of medium grade and 6 tons of medium-hard grade coal per day, and the deep mine produces 4 tons of medium grade and 8 tons of medium-hard grade coal every day. The company has a contract to deliver at least 600 tons of medium grade and 480 tons of medium-hard grade coal within 60 days. How many days should each mine be operated so that the contract can be filled at minimum cost?