Multiply the number of the person having the ring by 2; to that add 3. Multiply this by 5; then add 8 if the ring be on the right hand, or 9 if on the left. Then multiply by 10, and add the number of the finger (the thumb is 1); and, lastly, add 2.
Ask now for the result, from which subtract mentally 222, and the remainder will give the answer.
For instance, supposing the ring were put on the fourth person, on the left hand, and the first finger, remembering that the thumb counts 1.
The following is the kind of sum to be worked out:—
| The number of the person multiplied by 2 | 8 |
| Add 3 | 11 |
| Multiply by 5 | 55 |
| Add 9 for the left hand | 64 |
| Multiply by 10 | 640 |
| Add the number of the finger 2 | 642 |
| Add 2 | 644 |
| —— | |
| Subtract | 222 |
| —— | |
| 422 |
Which result proves it to be, beginning at the right-hand finger, the second finger of the left hand of the fourth person.
When the number of the person wearing the ring is above 9, the remainder will stand in four figures instead of three; in that case the first two will indicate the person.
Like all games of mental calculation, the more quickly this is done the better.