AMC 10 Step by Step
2009 AMC 10BProblem 19P16-20~4 minPrint

A particular 1212 -hour digital clock displays the hour and minute of a day. Unfortunately, whenever it is supposed to display a 11 , it mistakenly displays a 99 . For example, when it is 1:16 PM the clock incorrectly shows 9:96 PM. What fraction of the day will the clock show the correct time?

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Problem © Mathematical Association of America (MAA), American Mathematics Competitions. Reproduced for non-commercial educational use. Solution and commentary are original to this site.