4. 已知 \(X, Y\) 兩隨機變數的聯合機率分配如下表：

| Y | X | 1 | 2 | 3 | 4 |
| --- | --- | --- | --- | --- | --- |
| 1 | | 1/2P | P | 1/2P | 1/2P |
| 2 | | P | P | 1/2P | P |
| 3 | | 1/2P | 1/2P | P | P |

4-1. 請問 \(\mathbf{P}\) 為何？ \((4\%)\)