Question

A bungalow has one of its room located on the first floor and there are three identical 100 watt electrical bulbs fixed in the room. Each bulb is connected to a specific switch located at the basement. There are only three switches in the basement. All the bulbs are switched off at present and you are also at the basement area. The first floor cannot be seen from the basement area. If you are allowed to use your common prudence, what is the minimum number of times that you will have to go from basement to first floor to identify which switch goes to which bulb?

• A. 3 times
• B. 20 times
• C. 1 time
• D. 6 times

Answer 1

The Correct Option is C

To solve this problem, use logical reasoning to identify which switch corresponds to which bulb with the minimal number of trips upstairs. Follow these steps:

1. Turn on the first switch and leave it on for about 10 minutes. This allows the connected bulb to fully heat up.
2. After 10 minutes, turn off the first switch and immediately turn on the second switch.
3. Proceed to the first floor and check the bulbs in the room:

• The bulb that is lit is connected to the second switch, as it has been turned on most recently.
• The bulb that is off but warm to touch is connected to the first switch, having been left on for 10 minutes and then turned off.
• The bulb that is off and cool to touch is connected to the third switch, which was never turned on.

In this manner, you can determine which switch controls which bulb with only 1 trip to the first floor.