The thickness of the tube is given by: thickness = (external diameter − internal diameter) / 2 = (32 − 21) / 2 = 11 / 2 = 5.5 mm Let t = thickness = \(\frac{(D − d)}{2}\), where D = external diameter and d = internal diameter. The absolute error in thickness is found using the rules for propagation of errors (for subtraction and division by a constant): \Deltat = \(\frac{(\DeltaD + \Deltad)}{2}\) = \(\frac{(2 + 1)}{2}\) = \(\frac{3}{2}\) =1.5 mm. The percentage error in thickness is: Percentage error = \(\frac{\Deltat }{\text{t}}\) \times 100% = (\(\frac{1.5}{ 5.5}\)) \times 100% = (\(\frac{15}{ 55}\)) \times 100% = (\(\frac{3}{11}\)) \times 100% ≈ 27.27%