One hundred light bulbs
100 bulbs sit in a row, all off. Person 1 toggles every bulb; person 2 toggles every 2nd; person 3 every 3rd; … person 100 toggles only the 100th. After all 100 people have gone, how many bulbs are left on?
Show hints (2)+
- Bulb n is toggled once per divisor of n.
- Which numbers have an odd number of divisors?
Answer
Reveal answer →Final answer
10
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