Undergraduate Interview Questions

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The classic 100 light bulbs question: Light bulbs are numbered 1 to 100, and kept off initially. The first person comes and toggles all the bulbs which are multiple of 1, i.e. they switch all bulbs to 'ON'. The second person toggles all multiples of 2, i.e. they turn the even bulbs 'OFF'. The third person comes and toggles all multiples of 3. This process continues till the 100th person do their part. After this, how many bulbs are 'ON'?
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Undergraduate Engineer

Interviewed at Imperial College London

4.4
Nov 4, 2024

The classic 100 light bulbs question: Light bulbs are numbered 1 to 100, and kept off initially. The first person comes and toggles all the bulbs which are multiple of 1, i.e. they switch all bulbs to 'ON'. The second person toggles all multiples of 2, i.e. they turn the even bulbs 'OFF'. The third person comes and toggles all multiples of 3. This process continues till the 100th person do their part. After this, how many bulbs are 'ON'?

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