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 Switch Settlement (Posted on 2014-10-20)
Switch A turns lights 1 and 2 on/off or off/on
Switch B turns lights 2 and 4 on/off or off/on
Switch C turns lights 1 and 3 on/off or off/on
Switch D turns lights 3 and 4 on/off or off/on

```+-----+       +-----+
|  1  |       |  1  |
| OFF |       | OFF |
+-----+       +-----+
|  2  |       |  2  |
| OFF |       | ON  |
+-----+       +-----+
|  3  |       |  3  |
| OFF |       | OFF |
+-----+       +-----+
|  4  |       |  4  |
| OFF |       | ON  |
+-----+       +-----+

FIGURE 1      FIGURE 2```
Switches D, B, C and A are thrown in turn with result that Figure 1 turns into Figure 2. Each cell represents a given light and its state.

One of the switches does not work at all. Which one?

 No Solution Yet Submitted by K Sengupta No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
 Solution (different from previous) | Comment 2 of 3 |
Flipping all four switches should toggle each light twice.  So it they all start OFF they should all end OFF.
The fact that 2 and 4 are ON means they did not get toggled twice because Switch B does not work.

 Posted by Jer on 2014-10-20 08:48:17

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