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MathNet 2023-part-04 — 191 problems (EN–VI) Question 61

Math Olympiad Vault · MathNet 2023-part-04 — 191 problems (EN–VI)

Question 61

There is a power plant in the cell indicated by $C$. The cells indicated by $X$ are places to which the power plant should be connected. This requires electricity masts in some cells, which we can indicate by placing an $M$ in that cell. Two cells with a letter in them can be connected by a cable if the cells are adjacent at a side or a vertex. Ultimately, each cell with an $X$ must be connected to the power plant via one or more cells with the letters $M$ or $X$.

| $X$ | | $X$ | |
| | | | |
| | | | |
| $X$ | | | $X$ |
| | | | |
| $X$ | | $C$ | |
| | | | $X$ |

What is the minimum number of electricity masts needed?
A) 3 B) 4 C) 5 D) 8 E) 9