Negative allowance is provided on the pattern to take care of

Molten aluminium was poured in a sand mold and the thickness of solid skin formed after $$20$$ seconds and $$50$$ seconds were fond to be $$3mm$$ and $$4.5mm$$ respectively. What would be the thickness of the solid skin at the end of $$100$$ seconds after pouring?

Poor collapsibility of the mold leads to .......... type of casting defect in aluminium castings.

Green strength in powder metallurgy refers to the strength of