A casting of size $$100\,\,mm \times 100\,\,mm \times 50\,\,mm$$ is required. Assume volume shrinkage of casting $$2.6\% $$. If the height of the riser is $$80$$ $$mm$$ and riser volume desired is $$4$$ times the shrinkage in casting, what is the appropriate riser diameter in $$mm?$$

A $$10$$ $$mm$$ thick steel bar is to be horizontally cast with two correctly spaced top risers of adequate feeding capacity. Assuming end effect without chill, what should be the theoretical length of the bar?

The permeability of molding sand was determined using a saturated $$AFS$$ sample by passing $$2000cc$$ of air at a gage pressure of $$10$$ $$g/c{m^2}$$. If the time taken for the air to escape was $$1$$ min, the permeability number is: