The change in length for the rod is 20.11cm-20.05cm plus
the expansion of the steel ruler at its 20.11cm mark:
∆L = La∆T = (20.11 cm)(11 x 10-6 /C˚)(270˚C-20˚C)-- u should assume it
= 0.055 cm
∆L = (20.11cm-20.05cm) + 0.055 cm = 0.115 cm
The coefficient of thermal expansion of the material...