Steven S. Holland

Let’s say you have three light switches, one of which controls a single  light bulb hanging in the middle of a room.  The light switches are outside of the room, and with the door shut there is no way to see that the light is on — no light under the door, through a keyhole, nothing.

How can you tell which switch controls the light bulb if you can only enter the room once?

EDIT:

Solution: You turn on the first switch for a long time, say 10 minutes, then turn the switch off and turn on the second switch and immediately enter the room.

1.) if the light is on, the second switch is connected to the light.

2.) if the light is off, but the bulb is hot, it is the first switch.

3.) if the light is off, but the bulb is cold, the third switch is connected to the light.

My best solution is 2 weighings. I figure as this:you take 6 of the balls, and weigh 3 on each side. if they weith the same, then weigh the two remaining balls to find the heavier ball.

If they are different. then weigh two balls from the heavier set of three balls. If one is heavier than the other, there’s your heavier ball. if they weigh the same, than the 3rd, unweighed ball is your heaviest ball.

If you have 8 billiards balls, and one of them is heavier than the other 7 - given a balancing scale (where you compare the weight of something on one side of the scale to the other) what is the fewest number of times you need to weigh in order to find the heaviest ball?

I thought about this and came up with what I think is the right answer. I will post the answer tomorrow morning, Wednesday.