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Reading the digits from behind is the same as reflecting them in a vertical line of symmetry. This means $0$ and $8$ are read as themselves, and $2$ and $5$ are swapped. Note that the digits are read in the opposite order
Since the time is before 10:00, the first hour digit must be a 0. When read from behind, this means the last digit must also be a 0.
Since the time is between 3:00 and 10:00 and the second hour digit must be one that reads backwards as another digit, it must be either 5 or 8.
Since 08:80 is not a valid time, the time must be 05:20.
Reading from Behind
Age 11 to 14
ShortChallenge Level 
Reading the digits from behind is the same as reflecting them in a vertical line of symmetry. This means $0$ and $8$ are read as themselves, and $2$ and $5$ are swapped. Note that the digits are read in the opposite order
Since the time is before 10:00, the first hour digit must be a 0. When read from behind, this means the last digit must also be a 0.
Since the time is between 3:00 and 10:00 and the second hour digit must be one that reads backwards as another digit, it must be either 5 or 8.
Since 08:80 is not a valid time, the time must be 05:20.
This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.
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