SOLUTION: If all three iron bars have a width of 5cm and a length of 20 cm, which iron bar weighs the most? a) a hexagonal prism-shaped iron bar b) a rectangular prism-shaped iron bar c

That iron bar has the maximum weight, whose perpendicular section has the maximum area, under given condition.


Everybody having a bit of imagination will get that the rectangular prism-shaped iron bar has the maximum perpendicular section,
under given condition.  //  which is a SQUARE prism-shaped, in this case.



    Simply because other shapes are INSCRIBED into the square shape perpendicular section



Hence, . . .  // and you can make a simple logical conclusion on your own . . . 


ANSWER.  The rectangular prism-shaped iron bar.  //  which is a SQUARE prism-shaped, in this case.