Past exam of the mathematics course of the University of Cambridge / 2022 / ib / Paper 4 / 18H / b / Solution

A pure optimum is a saddle point: an entry minimal in its row and maximal in its column. In $A_1$, $c$ at $(2,1)$ is a saddle; in $A_2$, $c$ at $(2,2)$ is a saddle. Matrix $A_3$ has row maximin $b$ and column minimax $c$, so no saddle exists. Thus

Solved by gpt-5.6-sol high.