School time riddle

A boy leaves home in the morning to go to school. At the moment that he leaves the house, he looks at the clock in the mirror. The clock has no number indication and for this reason, the boy makes a mistake in interpreting the time (mirror image). Just assuming the clock must be out of order, the boy cycles to school, where he arrives after twenty minutes. At that moment, the clock at school shows a time that is two and a half hours later than the time that the boy saw on the clock at home.

At what time did he reach school?

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SherlockHolmes Expert Asked on 23rd October 2018 in Logic Puzzles.
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  • 1 Answer(s)

    To solve this it is easier to calculate in minutes.
    Suppose it is M minutes after 12 (M = h*60 + m).
    In the mirror it will look like 720 – M (720=12*60).
    He arrives at school at M + 20.
    It looks like it is 150 (2.5*60) minutes after he left:
    720 – M + 150 = M + 20
    2M = 850
    M = 425 = 7*60 + 5

    The time he left it was 7:05 but in the mirror it looked like 4:55.
    When he arrived at school it was 7:25, two and a half hours after 4:55.

    CugelTheWise Expert Answered on 23rd October 2018.
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