The volume of a rectangular bar is given by the formula:
Where l is the length and h is the height. if we multiply the height of the bar by 1/3, we get:
By replacing this new height in the formula of the volume of the bar, we get:
As we can see, when we multiply the height by 1/3 the same happens with the Volume, this means that the volume of the second bar (after taking 1/3 of its height) is one-third the volume of the first bar. Then the volume of the bar decreases.