Torsion. A flanged bolt coupling connects two shafts. The bolt circle diameter is 250 mm in which there are 12 bolts. The allowable shear stress is 55 MPa in the shafts and 23 MPa in the bolts. One shaft is hollow with outside diameter of 100 mm, while the other one is solid of diameter 50 mm. Determine the ratio of the outside and inside diameter of the hollow shaft and the bolt diameter so that both shafts and the flanged bolt coupling are having the same strength in torsion.