| Problem 20 Solution | |||||
| Time | Action | Time remaining before action | Time remaining after action | ||
| 4 Minute | 7 Minute | 4 Minute | 7 Minute | ||
| 0 | Turn over both hourglasses | 0 | 0 | 4 | 7 |
| 4 | Turn over 4 minute hourglass | 0 | 3 | 4 | 3 |
| 7 | Turn over 7 minute hourglass | 1 | 0 | 1 | 7 |
| 8 | Turn over 7 minute hourglass | 0 | 6 | 0 | 1 |
| 9 | Take egg off stove | 0 | 0 | 0 | 0 |
You can also try this problem witha a 15 minute egg and hourglasses of 7 and 11 minutes.
Thanks to The Grey Labyrinth for this one.
Michael Shackleford, A.S.A.