A cylindrical shell made of mild steel plate of 100 cm diameter is to be subjected to an internal pressure of 10 kg/cm^{2}. If the material yields at 2000 kg/cm^{2}, assuming factor of safety as four and using maximum principal stress theory, thickness of the plate will be

A plot of land 60°m x 20 m is measure steel tape. If the standard error of length width measurements is taken as ± 1 cm, the standard error of the area of the plot be