OGQR 2020: Question No. 102
Eight light bulbs numbered 1 through 8 are arranged in a circle as shown above. The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once. If the bulb numbered 1 flashes first, which numbered bulb will flash last?
| Source | OGQR 2020 |
| Type | Problem Solving |
| Topic | Number Properties |
| Sub-Topic | Basic |
| Difficulty | Easy – Medium |
Solution
Given
In this question, we are given
- Eight light bulbs numbered 1 through 8 are arranged in a circle, as shown in the diagram.
- The bulbs are wired so that every third bulb, counting in a clockwise direction, flashes until all bulbs have flashed once.
- The bulb numbered 1 flashes first.
To Find
We need to determine
- The number of the bulb that will flash last.
Approach & Working
As every third bulb is flashing, starting from bulb 1, we can determine the next bulbs as follows
- First: Bulb 1
- Second: Bulb 4
- Third: Bulb 7
- Fourth: Bulb 2
- Fifth: Bulb 5
- Sixth: Bulb 8
- Seventh: Bulb 3
- Eighth: Bulb 6
As we can see, all the eight bulbs are flashing at least once, and the last one to flash is bulb 6.
Hence, the correct answer is option D.
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