Question: A light bulb is hanging in a room. Outside of the room, there are three switches, of which only one is connected to the lamp. In the starting situation, all switches are 'off' and the bulb is not lit. If it is allowed to check in the room only once to see if the bulb is lit or not (this is not visible from the outside), how can you determine with which of the three switches the light bulb can be switched on?
Answer:
To find the correct switch (1, 2, or 3), turn switch 1 to 'on' and leave it like that for a few minutes. After that, you turn switch 1 back to 'off' and turn switch 2 to 'on'. Now enter the room. If the light bulb is lit, then you know that switch 2 is connected to it. If the bulb is not lit, then it has to be switch 1 or 3. Now touching for a short time the light bulb will give you the answer: If the bulb is still hot, then switch 1 was the correct one; if the bulb is cold, then it has to be switch 3.
From India, Madras
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1Answer:
To find the correct switch (1, 2, or 3), turn switch 1 to 'on' and leave it like that for a few minutes. After that, you turn switch 1 back to 'off' and turn switch 2 to 'on'. Now enter the room. If the light bulb is lit, then you know that switch 2 is connected to it. If the bulb is not lit, then it has to be switch 1 or 3. Now touching for a short time the light bulb will give you the answer: If the bulb is still hot, then switch 1 was the correct one; if the bulb is cold, then it has to be switch 3.
From India, Madras
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Brain Teasers
1. What is the easiest way to throw a ball, have it stop, and completely reverse direction after traveling a short distance?
2. What is at the beginning of eternity, the end of time, the beginning of every end, and the end of every place?
3. When things go wrong, what can you always count on?
4. What is always behind you but you can never touch it?
5. I am never the first to speak but I am always the last to be heard. Who am I?
6. We were born of the same mother, on the same day, at the same hour and in the same year. Yet we are not twins. How do you explain this?
7. Two fathers and two sons were seated round a table. There were four apples on the table. Each of them took one apple and ate it entirely yet there was still one apple left on the table. How was this possible?
8. Before Mount Everest was discovered which was the highest mountain in the world?
9. Here everything is not always in order. For example, Friday comes before Thursday, the cart comes before the horse, the driver comes before the employer. Where are we?
10. When I am alive I stay put where I am. It is only when I am dead that I move about here and there. Who am I?
11. How can you be behind a person when that person is also behind you?
Answers below:
1. Throw the ball straight up.
2. 'e'.
3. Your fingers.
4. The past.
5. An echo.
6. They are triplets.
7. There were only three persons at the table comprising a grandfather, his son, and his grandson.
8. Mount Everest, of course. It was always there!
9. In a dictionary.
10. A leaf.
11. Put yourself back to back of each other.
From India, Mumbai
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1. What is the easiest way to throw a ball, have it stop, and completely reverse direction after traveling a short distance?
2. What is at the beginning of eternity, the end of time, the beginning of every end, and the end of every place?
3. When things go wrong, what can you always count on?
4. What is always behind you but you can never touch it?
5. I am never the first to speak but I am always the last to be heard. Who am I?
6. We were born of the same mother, on the same day, at the same hour and in the same year. Yet we are not twins. How do you explain this?
7. Two fathers and two sons were seated round a table. There were four apples on the table. Each of them took one apple and ate it entirely yet there was still one apple left on the table. How was this possible?
8. Before Mount Everest was discovered which was the highest mountain in the world?
9. Here everything is not always in order. For example, Friday comes before Thursday, the cart comes before the horse, the driver comes before the employer. Where are we?
10. When I am alive I stay put where I am. It is only when I am dead that I move about here and there. Who am I?
11. How can you be behind a person when that person is also behind you?
Answers below:
1. Throw the ball straight up.
2. 'e'.
3. Your fingers.
4. The past.
5. An echo.
6. They are triplets.
7. There were only three persons at the table comprising a grandfather, his son, and his grandson.
8. Mount Everest, of course. It was always there!
9. In a dictionary.
10. A leaf.
11. Put yourself back to back of each other.
From India, Mumbai
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