A digital clock displays time in 24-hour format (HH:MM, from 00:00 to 23:59). How many times in a single 24-hour period does the display form a palindrome (reading the same forward and backward)?
16 times.
A palindrome requires MM to be the reverse of HH. For hours 00-05, valid minutes are 00, 10, 20, 30, 40, 50 (6 times). For hours 10-15, valid minutes are 01, 11, 21, 31, 41, 51 (6 times). For hours 20-23, valid minutes are 02, 12, 22, 32 (4 times). Hours 06-09 and 16-19 require invalid minutes of 60+. Total = 6 + 6 + 4 = 16 times.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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