## 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__

__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__

__To Find__

We need to determine

- The number of the bulb that will flash last.

__Approach & Working__

__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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