A biology lab stores petri dishes with bacterial cultures in three refrigerators, labeled A, B, and C. The table shows the number of dishes of each strain in each refrigerator.
| Refrigerator | Strain X | Strain Y | Total |
|---|---|---|---|
| A | 7 | 5 | 12 |
| B | 6 | 12 | 18 |
| C | 4 | 6 | 10 |
| Total | 17 | 23 | 40 |
One dish is selected at random from all 40 dishes. If the selected dish contains strain X, what is the probability that it came from refrigerator A?