The correct statement that identifies Hans's error is:
He did not finish the problem. He should have divided 1618 by 2 to find the square root.
This is incorrect because he should actually have taken the square root of 1618, but he does not need to divide by 2. The proper calculation for the hypotenuse \( c \) should be:
\[ c = \sqrt{9^2 + 40^2} = \sqrt{81 + 1600} = \sqrt{1681} = 41 \text{ cm}. \]
Thus, Hans's error lies in his misunderstanding of how to properly calculate the hypotenuse from the sum of the squares of the legs and then taking the square root of that result.