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A square section cantilever beam, 3 m in length, carries a concentrated load of 10 kN at its free end. If the maximum bending stress is not to exceed 30 MPa determine the minimum dimensions of the section.

Ans 182mm,

What would be the percentage saving in weight if a rectangular section beam, having a depth equal to twice its width, were to be used instead?

Intuitively it seems there would be a weight reduction of 50% if the width dimension was halved however I have the answer to be 29.6%, does somebody know how i would get to this?

Thanks