A stepped shaft with a major diameter of D = 2.50 in. and a minor diameter of d = 1.25 in. is subjected to a torque of 1,200 lb-in. If the maximum shear stress must not exceed 4,000 psi, determine the...

A stepped shaft with a major diameter of D = 2.50 in. and a minor diameter of d = 1.25 in. is subjected to a torque of 1,200 lb-in. If the maximum shear stress must not exceed 4,000 psi, determine the minimum radius r that may be used for a fillet at the junction of the two shaft segments. The fillet radius must be chosen as a multiple of 0.05 in.