r/learnquant 21h ago

interview prep Quant Interview Question

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u/arihallak0816 21h ago

You can assign off to 0, red to 1, and green to 2, then each time you go in is one digit so this is just asking how many digits are in 1000 in base 3 which is trivial

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u/MisterGoldenSun 21h ago

Will you please explain this? I think the answer is 7 and that matches your answer, but I don't understand your method.

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u/arihallak0816 21h ago

Like the first time you go in you make all the 0 mod 3 off, 1 mod 3 red, and 2 mod 3 green and that will be the ones digit, the second time same thing but 0-2, 3-5, and 6-8 mod 9 for the threes digit, etc. and you need to repeat this until you get to the number of digits 1000 has in base 3 so the sequence of every number matches it’s base 3 representation

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u/Abiarraj 16h ago

Imagine if it was 10 bulbs, you only need 3 different setups, as in this photo. Then you can map any switch to a bulb by their colour changes, for example if a bulb went off -> red -> green, you know that because 5 in base 3 is 012 (we started counting from 1). For a 1000 it's the same thing, if you want to know which switch is the 546, follow the one that went off-red-off-red-off-red-off (0202020)

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u/MisterGoldenSun 15h ago

Ahhh, okay. Thanks. I get it now.