Problem 4 · 2019 Math Kangaroo
Easy
Logic & Word Problems
careful-counting
A digital clock shows the time in the picture. What time is it when the clock next shows the exactly same digits again for the first time after that?
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Answer: C
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Hint 1 of 3
Read the four digits on the clock; the next time must use exactly those same four digits.
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Hint 2 of 3
A valid time needs hours from 00 to 23 and minutes from 00 to 59.
Still stuck? Show hint 3 →
Hint 3 of 3
Look for the earliest time after the shown one that is just a rearrangement of those four digits.
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Approach: find the next valid time that reuses digits 2,0,1,9
- The display 20:19 uses the digits 2, 0, 1, 9.
- We need the next time made of exactly these four digits, with a valid hour (00–23) and minutes (00–59).
- After 20:19 the first valid arrangement that appears is 21:09.
- So the answer is 21:09 (C).
Mark:
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