Time Puzzles & Riddles 1 : Clock Riddle
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What Time Should the last watch show ?
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Answer & Explanation
Solution:
5:19 Starting with the watch on the left, add 42 minutes to the time shown to give the time on the next watch to the right
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Time Puzzles & Riddles 2 : Classic Logical Interview Puzzle
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I have two rectangular wires.
Both of them have property that when i light the fire from one end , it will take 60 minutes to get completely burn.
However they do not burn at consistent speed (i.e it might be possible 1st 20% burn in 50 minutes and 80% can burn in 10 minutes).
So how could i measure 45 minutes ?
Answer & Explanation
Solution:
Steps:
A) burn 1st wire from both end and 2nd wire from one end
B) After 30 minutes(when 1st wire gets completely burned out) , burn the second wire from 2nd end as well
C) when 2nd run completely gets burned , you know its 45 minutes.
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Time Puzzles & Riddles 3 : Hour Glass Puzzle
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I have two sand hour glasses:
1. A 7 minute one and
2. An 11 minute one.
Using just these 2 sand hour glasses, how can i measure time as 15 minutes ?
Answer & Explanation
Solution:
1. Start both the 7 minute hour glass & 11 minute hour glass.
2. Wait till the 7 minute hour glass times out. Time is 7 minute!
3. Restart the 7 minute hour glass. At this time 11 minute hour glass will have 4 minutes left to time out.
4. As soon as 11 minute glass times out invert the 7 minute hour glass. Total time now is 11 minutes.
5. After inverting 7 minute hour glass, it will now have 4 minutes left for time out.
6. After these 4 minutes times out, the total time is 15 minutes.
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Time Puzzles & Riddles 4 : Logical Clock Problem
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Time in a digital clock can be palindromic like 12:12 (same when read forwards or backwards).
Whats the minimum interval between 2 times that are palindromic ?
Answer & Explanation
Solution:
2 minutes (between 9:59 and 10:01)
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Time Puzzles & Riddles 5 : Cross Bridge Puzzle
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Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for each person: 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?
Answer & Explanation
Solution:
17 mins
The initial solution most people will think of is to use the fastest person as an usher to guide everyone across. How long would that take? 10 + 1 + 7 + 1 + 2 = 21 mins. Is that it? No. That would make this question too simple even as a warm up question.
Let’s brainstorm a little further. To reduce the amount of time, we should find a way for 10 and 7 to go together. If they cross together, then we need one of them to come back to get the others. That would not be ideal. How do we get around that? Maybe we can have 1 waiting on the other side to bring the torch back. Ahaa, we are getting closer. The fastest way to get 1 across and be back is to use 2 to usher 1 across. So let’s put all this together.
1 and 2 go cross
2 comes back
7 and 10 go across
1 comes back
1 and 2 go across (done)
Total time = 2 + 2 + 10 + 1 + 2 = 17 mins
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Time Puzzles & Riddles 6 : Maths Time Puzzle
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A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 3 hours to fill the tank with the large inlet pipe. On the other hand, it takes 6 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 9 hours.
What fraction of the tank (initially empty) will be filled in 0.64 hours if all three pipes are in operation? Give your answer to two decimal places (e.g., 0.25, 0.5, or 0.75).
Answer & Explanation
Solution:
In one hour,
Soln 1:
the large inlet pipe fills 1 / 3 of the tank;
the small inlet pipe fills 1 / 6 of the tank;
the outlet pipe empties 1 / 9 of the tank; and therefore
all three pipes together fill [ (1 / 3) + (1 / 6) − (1 / 9) ] of the tank.
Fraction of the tank that will be filled in 0.64 hours =
0.64 [ (1 / 3) + (1 / 6) − (1 / 9) ] = 0.25.
Soln 2:
Let V be the total volume of the tank. From equation (1),
Flow Rate (large inlet pipe) = V / 3
Flow Rate (small inlet pipe) = V / 6
Flow Rate (outlet pipe) = V / 9.
Substituting in equation (2),
Rate of Accumulation in tank = (V / 3) + (V / 6) − (V / 9).
Using the above result in equation (1),
Time required to fill the complete tank = V / [ (V / 3) + (V / 6) − (V / 9) ].
Note that V cancels out on simplifying the above expression.
Fraction of the tank that will be filled in 0.64 hours =
0.64 [ (1 / 3) + (1 / 6) − (1 / 9) ] = 0.25.
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Time Puzzles & Riddles 7 : What Is Time Riddle
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I noticed that in my big wall clock , there is a time when the minute and hour clock are exactly between one and two.
Also i notice both hands lie on top of each other.
What is the time i am talking about ?
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Answer & Explanation
Solution:
12:00
both minute and hour clock lie exactly between the number one and two in the number
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Time Puzzles & Riddles 8 : Measuring Time Interview Problem
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I possess two wires. Both of them have an inconstant thickness but both of them burns completely in sixty minutes. The problem is that I want to measure forty-five minutes while using these two wires.
How can I measure if cutting the wire in half is not possible due to non-homogeneous construction ?
Answer & Explanation
Solution:
45minutes
It is not as hard as it seems. I will burn one wire on both ends and the other wire at one end only. The first wire will burn completely in thirty minutes and at that very moment, I will burn the other end of the second wire and it will burn in fifteen minutes. Thus both of the wires will be burnt in 30 + 15 = 45 minutes.
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Time Puzzles & Riddles 9 : Infosys IQ Interview Question
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You are frying fishes on a pan which can accommodate only 2 fishes at one time. It takes 5 minutes to fry one side of the fish.
What is the shortest time in which you can fry 3 fishes in the same pan ?
Answer & Explanation
Solution:
15 minutes.
Put 2 fishes in the pan. Fry for 5 minutes and then take out one and turn the other one. Also put in the third fish. Now fry for 5 minutes. The fish that you turned must be ready now so take it off while turning the other one. Also put in the fish which was fried from one side only in the pan. Fry them for 5 minutes and all the three fishes are fried now.
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Time Puzzles & Riddles 10 : September Riddle
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man gave one son 10 cents and another son was given 15 cents. What time is it?
Answer & Explanation
Solution:
1:45.
The man gave away a total of 25 cents. He divided it between two people. Therefore, he gave a quarter to two
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Time Puzzles & Riddles 11 : Faulty Clock Problem
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A clock loses 10 minutes each hour.If the clock is set correctly at noon,what time is it when it reads 3 PM ?
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Answer & Explanation
Solution:
3:36 PM.
The clock loses 10 minutes each hour,
so it loses 5 minutes every half-hour,
and it loses 1 minute very 6 minutes.
It is 12:50 PM at 1:00 o'clock.
It is 1:40 PM at 2:00 o'clock.
It is 2:30 PM at 3:00 o'clock.
It is 2:55 PM at 3:30 o'clock.
It is 3:00 PM at 3:36 o'clock.
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Time Puzzles & Riddles 12 : Logical Valentine Day Lucky Problem
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Katrina, kareena, Priyanka and Deepika visited me on the valentine's Eve.
The time of each visit is mentioned below:
A) Katrina at 8:00
B) kareena at 9:00
C) Priyanka at 10:00
D) Deepika at 11:00
*Each time mentioned above may be either AM or PM.
Also below statements hold true:
A) Priyanka did not visit me between kareena and Deepika.
B) At least one female visited me between Katrina and kareena.
C) Katrina did not visit me before both Priyanka and Deepika.
Can you tell at what time did they individually visit me ?
Answer & Explanation
Solution:
kareena (9:00AM) - Deepika (11:00AM) - Katrina (8:00PM) - Priyanka (10:00PM)
From the given data, it is clear that at least one female visited me in the morning and at least one female visited me in the evening. Also, from (4), Katrina did not visit me first. It means that Katrina visited me at 8:00 PM. From (3), kareena must have visited me at 9:00 AM. Also, either Priyanka or Deepika or both visited me in the morning. But from (2), only Deepika must have visited me in the morning at 11:00 AM and hence, Priyanka visited me at 10:00 PM.
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Time Puzzles & Riddles 13 : Horse Wind Puzzle
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Emily learnt how to ride a horse recently. Just to test her skills, she rode the horse from her home till a mine which she covered in three minutes and returned back home from the same path only this time she took four minutes. The reason was that while riding away from home, she was supported by wind however while riding back, she was riding against the wind.
How fast do you think she could have rode a mile if there was no wind ?
Answer & Explanation
Solution:
3 minutes and 25 5/7 seconds.
The most common way how most of people see this problem is adding 3 and four to obtain 7 and they believe it should give a correct average and thus her time should be taken to 3 and half minutes. But if you do like that, you will get to a wrong answer. This is because, the wind has only helped her for three minutes while it has worked against her for four minutes.
If she could ride a mile in three minutes with the wind, it is evident that she could go a mile and 1/3 of a mile in four minutes. Thus two and 1/3 miles in eight minutes will give her actual speed as the wind has helped her as much as it has worked against her.
Thus her actual time for a single mile without wind will be 3 minutes and 25 5/7 seconds.
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Time Puzzles & Riddles 14 : Math Logic Problem
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In a modern art gallery, an artist has numerous modern art paintings created by him. He hangs different painting on the space provided to him periodically. When the clock hit 11 am, he hung the painting number 30. When it struck 4 pm, he hung the painting number 240 and when it struck 7:30 pm, he hung painting number 315.
Can you determine, which painting number will he hang when the time is 9:20 pm ?
Answer & Explanation
Solution:
He will hang painting number 200 at that time. Every time he hangs the painting, the number of it corresponds with the angle between the minute and hour hand of the clocks.
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