Question 8
The magician Bibrax puts 49 coins on a table. Bibrax closes his eyes and asks a beaver to turn over any one coin. On opening his eyes, Bibrax can tell the beaver which coin was turned over. The secret of the trick is: “the number of star-side-up coins in each row and each column is initially even”.
Editable transcription (1=star, 0=blank):
| | A | B | C | D | E | F | G |
|---|---|---|---|---|---|---|---|
| 1 | 0 | 1 | 0 | 1 | 0 | 1 | 1 |
| 2 | 1 | 0 | 0 | 0 | 1 | 1 | 1 |
| 3 | 1 | 0 | 1 | 1 | 0 | 1 | 0 |
| 4 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 5 | 0 | 1 | 0 | 1 | 1 | 1 | 0 |
| 6 | 1 | 0 | 1 | 1 | 0 | 1 | 1 |
| 7 | 0 | 0 | 0 | 1 | 0 | 0 | 1 |
Which coin did the beaver turn over in the picture above?
Editable transcription (1=star, 0=blank):
| | A | B | C | D | E | F | G |
|---|---|---|---|---|---|---|---|
| 1 | 0 | 1 | 0 | 1 | 0 | 1 | 1 |
| 2 | 1 | 0 | 0 | 0 | 1 | 1 | 1 |
| 3 | 1 | 0 | 1 | 1 | 0 | 1 | 0 |
| 4 | 1 | 0 | 0 | 0 | 0 | 1 | 0 |
| 5 | 0 | 1 | 0 | 1 | 1 | 1 | 0 |
| 6 | 1 | 0 | 1 | 1 | 0 | 1 | 1 |
| 7 | 0 | 0 | 0 | 1 | 0 | 0 | 1 |
Which coin did the beaver turn over in the picture above?