- The answer on the website: 1406
- My answer: 1404
I know that the starting question of day 1 is 470, then it reduces to 469 and continues until day 3, where the starting question is 467 and the ending question is 469. In the solution, it stated that on day 1404, there are 2 questions left to do. However, because 1404 is divisible by 3, the actual ending question is actually 2 more than the stated question, so the starting question is 0 after the student has completed it.
I have done this question twice using two different methods:
- Creating an easier example: I’m brute forcing when trying with the initial number of questions is only 4,5, and 6, and get the result of 6, 9, and 12 days respectively.
- Then I can quite confident that the result = (the number of question) * 3 - 6
- I’m using Excel to brute force 470 questions from day 1 until day 1410.
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Start of day = End of day before minus 1.
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End of day = Start of day, if the day is divisible by 3, then it is plus 2.
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So the first time that the question is reduced to 0 is 1404, where it’s 1 question left on day 1403, and she has already done that question earlier on day 1404.
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