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Question 1120234: How often in a 12- hour period of time does the sum of the digits on a digital clock equal 9?
Found 2 solutions by Alan3354, greenestamps:
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! How often in a 12- hour period of time does the sum of the digits on a digital clock equal 9?
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Is it hours and minutes? Or seconds, too?
eg, 12:33 or 12:33:00 and 12:30:03
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What is the starting time?
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Is it a 12 hour clock, or 24 hour?
eg, 15:03 or 15:01:02
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I use 24 hours, I find AM and PM irritating, and more likely to cause problems.
I was staying at my in-laws in CA, and had to make a flight out of SFO at 0600 (6 AM), which is 60 miles away, the next day.
They gave me an alarm clock to use, and I set it for 4:30. I didn't notice some sort of AM/PM indicator and I set it for 4:30 PM by mistake.
Had it used 24 hours, the difference between 0430 and 1630 would have been obvious.
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There is NO advantage to AM/PM, but there are some disadvantages.
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A place I worked years ago had a time clock for hourly employees. Once someone was shorted 12 hours pay because of the AM/PM business. He wasn't happy, tho it was eventually corrected.
NEVER get a time clock using AM/PM. The time from 0759 to 1659 is obviously 9 hours.
From 7:59 AM to 4:59 PM is not so obvious.
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PS Ask me about Zulu time.
Answer by greenestamps(13195)  (Show Source):
You can put this solution on YOUR website!
I will assume that the digital clock is a 12-hour clock that shows only hours and minutes, since that is by far the most common kind.
There is no significant shortcut to the answer. Simply make a list of the different times, probably starting at 12:00 and going to 11:59.
12:06, 12:15, 12:24, 12:33, 12:42, 12:51
1:08, 1:17, 1:26, 1:35, 1:44, 1:53
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11:07, 11:16, 11:25, 11:34, 11:43, 11:52
You can save a little time by looking for patterns, remembering that the number of minutes has to be less than 60.
I counted a total of 57 times; but I could easily have mis-counted....
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