r/mathriddles • u/hawking_s • 19d ago
Medium Solve real life Clock riddle?
Can you work this out? This actually happened in my kitchen when I was a teenager.
When I went to bed, at 11pm, all three clocks in the kitchen were working and said the correct time: 11pm.
When I woke and went into the kitchen for breakfast, all three clocks were working, yet one said 5am, one said 6am and the third said 7am. No one had touched them.
Why? How? What happened and when? And what was the correct time when I went down for breakfast?
SOLUTION:
(Congrats u/RealHuman_NotAShrew)
There was a power cut for one hour at 1am. The battery powered clock on the wall continued unaffected. The analogue clock on the oven froze for the hour then resumed at 2am, one hour behind. The digital clock on the microwave turned off at 1pm then reset at 2am to 00:00. 2 hours behind. At 7am, the wall clock said 7am, the analogue clock on the oven said 6am and the microwave clock said 5am.
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u/Dragofant 19d ago edited 19d ago
Clock A is battery driven, Clock B is powered by the grid, Clock C is connected to the internet.
At 1 am you had a short power outage, and Clock B resets to 12pm. At 2 am Clock C shifts to summertime, which is 3am.
Clock C was showing the correct time (7am) when you had breakfast.
E: spoiler formatting
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u/Riegel_Haribo 19d ago
This is low in math, since given a time 5am, you only need to come up with the number five.
Lets imagine the abundance of clocks are on appliances, instead of someone time-obsessed, and are wall powered.
The appliances have internal DC power supplies for the clocks powered by wall power. Capacitance and power reserve during the phase reversal of AC voltage is required in such a supply. The appliance power supplies have different amount of reserve power capacities to sustain clock operation over a brief power outage bump. The only unlikely but possible happenstance is the preciseness of timing if all clocks remain perfectly aligned to the minute with only exact hour offsets.
The setting is more than a solution for you to determine how long ago two most recent power outages with effect happened (or three if no time is correct).
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u/RealHuman_NotAShrew 19d ago
There are quite a few possible solutions I can come up with; here's one that doesn't require
a daylight savings time change
Three clocks: one analog plugged in to an outlet, one digital connected to an outlet, and one running on battery power. House loses power at 1am for exactly one hour. At 2am the analog clock picks up where it left off, so it's an hour behind. The digital clock resets to midnight, so it's two hours behind. The battery-powered clock never stopped, so it displays the correct time.