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2023 Math Kangaroo

Problem 5

Problem 5 · 2023 Math Kangaroo Medium
Number Theory divisibilitymod-10

Today is Thursday. What day of the week is it in 2023 days?

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Answer: C — Thursday
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Hint 1 of 2
The days of the week repeat every 7 days.
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Hint 2 of 2
Find the remainder when 2023 is divided by 7.
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Approach: count days modulo 7
  1. Days repeat with period 7, so only 2023 mod 7 matters.
  2. 2023 = 7 · 289, which leaves remainder 0.
  3. A whole number of weeks lands on the same weekday.
  4. So it is still Thursday.
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