Let L, B and H be the base length, base width and height of rectangular prism/ pyramid.
Volume of prism, V₁ = LBH
Volume of pyramid, V₂ = (LBH)/3
Total volume of water in 2 full rectangular pyramids = 2 [(LBH)/3]= (2/3)V₁
This is equivalent to 2/3 of volume of prism.
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