Wall thickness from diameter difference Steps:

• Subtract internal diameter from external: 12.0 mm - 10.0 mm = 2.0 mm (diameter difference).
• Divide by 2 for wall thickness (one wall on each side): 2.0 mm / 2 = 1.0 mm.
• Add uncertainties for subtraction: 0.1 mm + 0.1 mm = 0.2 mm (for difference).
• Halve uncertainty for thickness: 0.2 mm / 2 = 0.1 mm. Why A is correct:
• Matches formula t = (d_e - d_i)/2 with worst-case uncertainty propagation (addition then scaling). Why the others are wrong:
• B: Uses full difference as thickness, ignoring division by 2.
• C: Halves thickness but applies full added uncertainty to it.
• D: Treats full difference as thickness with added uncertainty.

Final answer: A