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Production Function for a Wheat Farm Wheat Output (tonner) Number of Workers The upper part of within the coordinate range (3,25) to (6 and 7,42) where output is , is and corresponds to the zone of progressively O maximized, concave downward, declining marginal productivity maximized, concave upward, declining marginal productivity minimized, convex upward, increasing marginal productivity OO minimized, convex downward, increasing marginal productivity