First find the weight of food Karen eats every hour: 2 pounds * 1/3 = 2/3 pounds food.
Then find the total amount of weight Karen's backpack loses per hour she hikes: 2 pounds water/hour + 2/3 pound food/hour = 8/3 pounds/hour.
Multiply this by the number of hours she hikes to find the total amount of weight she loses: 8/3 pounds/hour * 6 hours = <<8/3*6=16>>16 pounds.
Add the weight of all her items to find total starting weight: 20 pounds + 10 pounds + 20 pounds = <<20+10+20=50>>50 pounds.
Then subtract the weight she loses from the starting weight to find the weight after 6 hours: 50 pounds - 16 pounds = <<50-16=34>>34 pounds
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