If you were to grill two hamburgers at the same it would take 5 minutes to grill one side of 2 hamburgers and ten minutes to grill 2 ham burgers on both sides. So 10 minutes would make two hamburgers while 20 minutes will cook 4 hamburgers than add and extra 10 minutes to cook the last hamburger on both sides.
10 minutes = 2 both side cooked hamburgers
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10 minutes = 2 both side cooked hamburgers
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an extra 10 minutes = another both side cooked hamburgers since we only need five
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30 minutes in minimal time to cook five hamburgers
