Questions tagged [time]

Puzzles which include the concept of time, as for instance: clocks, dates, calendars, conversions from one time zone to another, time-intervals.

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39
votes
5answers
5k views

Burning ropes as timers

You have 2 identical ropes which burn at a specific rate, and an unlimited supply of matches. When you light one end of a rope, the fire will take exactly 1 hour to travel to the other end of the rope....
32
votes
16answers
11k views

Older twin's birthday is one day after younger's

I have been asked this puzzle in an interview. There was not a lot of time left so I couldn't solve it quickly and the interviewer kind of let it go as he had to wrap up the interview Foo and Bar ...
6
votes
7answers
17k views

A man is born in 1955

(I heard this in a movie and I think it’s pretty cool.) A man is born in 1955. Today, the 14th of August, 2017, he is 18. How is this possible?
12
votes
3answers
812 views

Day and night of the two timers

            Make a non - 24 - hour day /  night cycle       &...
7
votes
3answers
735 views

Odd hours with two timers

Two motorized 24-hour light timers are daisy chained between a power outlet and a light bulb. For these timers, devise schedules and choose initial times that produce the following repeated 9-hour ...
9
votes
2answers
358 views

Third timer's a charm

Three motorized 24-hour light timers are arranged between a power outlet and a light bulb, with timer A parallel to a daisy chain of timers B and  C. For these timers, devise schedules that ...
8
votes
3answers
538 views

Halve time with two timers

Two motorized 24-hour light timers are daisy chained between a power outlet and a light bulb. For these timers, devise schedules and choose initial times that produce the following repeated lighting ...
7
votes
5answers
15k views

Meeting of hands on a clock

We have a regular analog clock with three hands - second, minute and hour. On a given day, how many times do: (a) the minute and hour hands (b) the minute and second hands (c) the hour and second ...
9
votes
3answers
2k views

Missed appointment

The story This story occurs not far from Liège, in Belgium. We are January 1st, 2013. Two bad men prepare the attack of a train. To do this, they set an appointment, during the year, at 2:30 a.m., ...
11
votes
2answers
445 views

Another Twin Puzzle: Three Days Difference

Today is my first day joining my college's Puzzle Club. It is so much fun gathering in a group with similar interests! I meet a lot of new friends and of course asked their contact number to discuss ...
6
votes
6answers
3k views

Timepieces and Moving Parts

The sundial keeps time with the fewest number of moving parts. Which timepiece has the most moving parts?
4
votes
1answer
489 views

Connecting 3 circular power timers to lights so that they turn for one day on Christmas

My friend gave a question to me. I am not sure if it is an original puzzle, but he has 2 lines of Christmas lights and 3 circular timers with 96 switches apiece. Each switch turns on power for 15 ...
4
votes
4answers
2k views

An Hourglass Puzzle

This puzzle follows from the well known sand timer puzzles: A Sand Timer Challenge http://www.crazyforcode.com/sand-timer-puzzle/ http://www.cut-the-knot.org/hg_solution.shtml Warmup: You are given a ...
13
votes
3answers
838 views

One More Twin Puzzle: Four Days Difference?

This is updated version for Another Twin Puzzle: Three Days Difference Today is my first day joining my college's Puzzle Club. It is so much fun gathering in a group with similar interests! I meet a ...