## Wednesday, December 2, 2009

### Midnight Arithmetic

My husband brought from somewhere this old digital clock with bright LED digits that are clearly visible at night. This clock has been running one hour ahead ever since we switched back from the daylight saving time on November 1st. Every part of the clock - hour digits, minute digits - is controlled via separate buttons. The hour button is stuck, making it impossible to adjust to the standard time:

For a month we have been waking up, looking at the clock, panicking if it is too late, then remembering the extra hour, and taking it away from what we see. We may have continued this ridiculous midnight subtractions for another half a year, if suddenly it would not occur to me that there is a simple way to adjust the clock. Even with the stuck hour button. Guess, what is it?

Please explain your answer on our Family Puzzle Marathon site. Solve three puzzles and get a prize!

Kim said...

We have that same clock. Unplug it! (and remove the battery if there's one in there) It will read 12:00. Depending on whether it defaults to AM or PM, plug it in at noon or midnight exactly.

W said...

I think this is another way of doing it:

Wait until the end of an hour (say 2:59). The time will actually be 1:59. Press the minute button so that it reads 2:00 (before it hits 3). By the time the actual time hits 2:00, you'll most likely be at 2:01 (resetting the time and letting a minute pass while doing so). Simply press the minute button until it reads 2:00 and it will be the right time.

Maria said...

You guys are amazing!
The approach I used was the second one, suggested by W. But Kim's idea is also great.
You both deserve a point.
This is a great puzzle to share with your kids. My nine year old son was able to figure it out when I forced him to sit in front of this clock :) You can trick your kids by changing one of the digital clocks at home to run ahead.
New puzzle and a newsletter tomorrow.