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In case not discussed before, I have the following alternative Solution to the Clock-in-the-mirror puzzle:
Solution:
- The mirror inverts the clock 180 deg around the 12-6 hrs vertical Axis.
- Let Tm and Td denote the mirror and departure times, respectively,
Then the effect of the inversion is such that:
Tm+Td = 12 for all times around the vertical axis
Or Td = 12 -Tm ........................(1)
- Let Ta denote the arrival time
- Given:
Td+20/60 =Ta ......................(2)
Tm=Ta-2.5 ..........................(3)
Now, substituting (3) into (1) and substituting for Td in (2), we get
Tc =12-Tc+2.5+20/60
=> Tc = 7.416666666667 hours
= 7hrs + (0.41666667*60min)
= 7:25