# 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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11k views

### A clock correct three times a day

A stopped clock tells the right time twice a day. How fast must a clock go for it to be right three times a day?
6k 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....
9k views

### Measure 22 minutes with 7 and 13 minute hourglasses

You have two hourglass timers. One can measure 7 minutes and the other hourglass timer can measure 13 minutes. This means that it takes 7 minutes for the sand timer to completely empty the sand from ...
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 ...
13k views

### Born on the same day, but one is two years older

Two people were born on the same day, same year, and share the same birthday. One is 2 years old, the other is only a few days old. What's going on here?
2k views

### Digital Clock Brightness

My alarm clock has a typical 7-segment digital display showing hours and minutes. Every lit segment is equally bright, and every unlit segment is equally dark. The separator (:) is always lit. ...
1k views

### Aging A Lot Faster

The day before yesterday, I was 20 years old, and next year I will turn 23. What day is it today? Note: This is not lateral-thinking, and the solution is real and ...
11k views

### My birthday is uncommon

I was born 1 day after my sibling. Yesterday was my sibling's birthday but today is not my birthday. When is my birthday?
4k views

### A weird and spooky clock

Out of nowhere, a clock appeared on my desktop: (you don't have to be able to view the GIF in order to solve it, I think the "preview" image gives you all the minor clues hidden in it. I also ...
2k views

### Two brothers, two watches

Two brothers, Jack and Joe, were born in May. One was born in 1932, and the other, a year later. Each brother owned a watch, which was previously possessed by their father. Considering their age, ...
2k views

### Finally, you wake up from a coma

You can barely open your eyes when a doctor walks up to you: You are a lucky one. Not many people have survived an accident like this. Only a handful of neurosurgeons are able to perform such an ...
499 views

### “Musical chair” for clock hands

A colleague and me usually make bets on the time when a simulation is finished. Next time I would suggest the following: At the time the simulation is finished we take a look at the analog clock on ...
3k views

### How often does a digital watch show a palindrome?

A palindrome is a word, phrase, number, or other sequence of characters which reads the same backward or forward, such as madam or kayak. We have a digital watch showing the time HH:MM:SS as shown in ...
860 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 ...
1k views

### Visiting the gym this month

Question Three men visit a gym on a regular basis - one every two days, one every three days, and the last one visits once every week (on the same day). In a particular month, one of the 3 men's ...
354 views

### You cannot have 120 degrees of separation, but how close can you get?

If you take a look at a standard three-hand gear-driven analog clock, there is never(see footnote) a time of day where the hands of the clock divide the face equally into 120 degree segments, but you ...
826 views

### Day and night of the two timers

Make a non - 24 - hour day /  night cycle       &...
3k views

### This puzzle is late!

I meant to release this puzzle 15¼ hours ago, and forgot again just over 9⅓ hours ago. But don't worry, it's fine. The puzzle is finally out. What is this puzzle about? NB: What timezone I am ...
700 views

### Short Puzzle: Graphic Painting

The artist in the market is giving this painting for free (the last one on his rack). I asked him if I can take it but he replied "Why should I give it to you?" The frame could be useful but I dont ...
2k views

### When was I born?

I was born just 10 minutes apart from my twin brother, but I celebrated my birthday 11 days after my twin brother every year. When was I born ?
454 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 ...
662 views

### Mirrored clocks

Triangulating for the simplest puzzle that is still at least somewhat interesting to solve.. On the left side wall in this picture, we have two particular clocks: 1: an analog clock with identical ...
841 views

### How to rephrase this puzzle about a meditating monk and incense

Here's a math-flavored puzzle I found on Andrej Cherkaev's website that I like to give to my undergraduate math students. I've paraphrased it to try to make it clearer: A monk was instructed by his ...
2k views

### A mosquito is born at T=0 and after 2 seconds makes a new mosquito every second, how many mosquitos at T=8.5? [closed]

One mosquito is born at T=0 and after 2 seconds it makes a new mosquito, and another every second thereafter. All such mosquitoes have this same property and do not die. How many mosquitoes there are ...
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., ...
486 views

### A Final Twins Puzzle: Twelve Days Difference?

Inspired by @athin's One More Twin Puzzle: Four Days Difference? After reading @athin's question, I was inspired to ask my own puzzle club about their birthdays. One of the members, Ethan, surprised ...
273 views

### Where are you at this time

Where are you if, When it's 10 o'clock, it's 2 o'clock When it's 5 o'clock, it's 7 o'clock
365 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 ...
17k 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 ...
554 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 ...
711 views

### One a puzzle, two a puzzle, Hot Cross Clocks

It's Good Friday! I want to make perfect hot cross buns by superimposing two 12-hour clock faces on top of each other. Is this possible, and if so, how many ways are there of doing so? In other ...
751 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 ...
332 views

### How many dates are ambiguous across the Atlantic?

The Day/Month/Year date system commonly used in Britain (and much of Europe?) and the Month/Day/Year system commonly used in the US can lead to confusion when, for example, we write 9/3/2018 for the ...
255 views

### What is it this Time?

Most clocks tell the time, but some are for letters. ...
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?
3k views

### Full-sized ice cubes

On a table in front of you is a small freezer that is capable of holding seven standard ice cube trays stacked on top of each other. There are no shelves to separate the trays, and if you stack one ...
3k views

### Timepieces and Moving Parts

The sundial keeps time with the fewest number of moving parts. Which timepiece has the most moving parts?
700 views

### Ages of A and B (self-reference in past)

A says to B My age is twice of what your age was when I was of your age. B says to A If you add your current age to twice of your age when I was born, the answer is $63$. Assuming they both ...
1k views

### What's Bob's age again?

I created this problem myself, but I did have inspiration. Today is a special day, I'm moving out of my parent's house. My father comes to me and says "Wow, you're half my age. On the day we moved ...
921 views

### A time-traveller's puzzle

Intense and long story coming up... In a galaxy, far, far away there lived a population of creatures, human-like but definitely smarter. The whole galaxy experienced three phases for every Earth ...
761 views

### What timezone am I?

It was 17:52 in the evening and I couldn’t wait for my class to finish. Only 8 more minutes… I really hate night school! I sat there pondering the stuff on the blackboard and wondering why he wrote ...
208 views

### A Second Hand Question

" It is a very simple question", said Grandpa " Look at that wall clock and tell me exactly how many times the Second Hand passes directly over the Minute and the Hour Hands in a 24 hour period....
237 views

### Switching the clock

"Observe the time, would you, Watson, old chap?" I did as instructed and glanced at the large grandfather clock standing in the corner. "Just a little after 4.42, Holmes." He nodded, "So when the ...