This question already has an answer here:
The base area and water depth is supposed to be the same for all three containers.
The pressure in a static fluid arises from the weight of the fluid and is given by the expression $P=\rho gh$.
The expression tells us that the fluid pressure at the bottom of all three containers is the same because the depth is the same.
If the pressure is the same then the normal force exerted by the bottom of the container on the fluid is the same since $F = P\times A$. But the normal force is also equal to the weight of the fluid which is different for all three containers. How is this possible? While I was trying to find an answer to this question on the internet, I found a couple of forums that said the reaction forces from the sides of the containers are responsible for this, but I can't see exactly how.
If anyone could show the math of how that would work out, that would be helpful.