### BdMO National 2012: Junior 7, Primary 9

Posted:

**Sun Feb 12, 2012 9:22 am****Problem:**

Each room of the Magic Castle has exactly one door. The rooms are designed such that when you can go from one room to the next one through a door, the second room's length is equal to the first room's width, and the second room's width is half of the first room's width (see the figure). Each door can be used only once. Magic Prince has entered the castle and now needs to get out. To get out of each room, the prince needs time equal to the width of the room. The prince has to use each door to get out of the castle. Due to the blessings of a Sufi, the prince can become as small as he wants (so that he can go into even very small rooms). If the castle is a square of side length $20$ meters then how long will it take for the prince to get out?