From the article: "¶Look for cages whose target numbers are unusually high or low for their number of squares. Often these have unique answers. For example, in

From the article: "¶Look for cages whose target numbers are unusually high or low for their number of squares. Often these have unique answers. For example, in a six-by-six puzzle, two squares with a sum of 11 must be filled with 5 and 6, in some order. Three squares with a product of 10 must be 1, 2 and 5." Why must two squares with a sum of 11 be filled with 5 and 6?