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5 Hardest Logic Puzzles

Top 5 Hardest Logic Puzzles

Logic Riddles 1 : Aeroplane Hardest Quiz
Difficulty ★★★★★     Popularity ★★★☆☆

The puzzle question is : On Bagshot Island, there is an airport. The airport is the homebase of an unlimited number of identical airplanes. Each airplane has a fuel capacity to allow it to fly exactly 1/2 way around the world, along a great circle. The planes have the ability to refuel in flight without loss of speed or spillage of fuel. Though the fuel is unlimited, the island is the only source of fuel.
What is the fewest number of aircraft necessary to get one plane all the way around the world assuming that all of the aircraft must return safely to the airport? How did you get to your answer?
(a) Each airplane must depart and return to the same airport, and that is the only airport they can land and refuel on ground.
(b) Each airplane must have enough fuel to return to airport.
(c) The time and fuel consumption of refueling can be ignored. (so we can also assume that one airplane can refuel more than one airplanes in air at the same time.)
(d) The amount of fuel airplanes carrying can be zero as long as the other airplane is refueling these airplanes. What is the fewest number of airplanes and number of tanks of fuel needed to accomplish this work? (we only need airplane to go around the world)

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Logic Riddles 2 : Challenging Mind puzzles
Difficulty ★★★★★     Popularity ★★★★☆

You are the ruler of a medieval empire and you are about to have a celebration tomorrow. The celebration is the most important party you have ever hosted. You've got 1000 bottles of wine you were planning to open for the celebration, but you find out that one of them is poisoned.

The poison exhibits no symptoms until death. Death occurs within ten to twenty hours after consuming even the minutest amount of poison.

You have over a thousand slaves at your disposal and just under 24 hours to determine which single bottle is poisoned.

You have a handful of prisoners about to be executed, and it would mar your celebration to have anyone else killed.

What is the smallest number of prisoners you must have to drink from the bottles to be absolutely sure to find the poisoned bottle within 24 hours?

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Logic Riddles 3 : Hardest Balance Logic Puzzle
Difficulty ★★★★★     Popularity ★★★★★

You are given a set of scales and 12 marbles. The scales are of the old balance variety. That is, a small dish hangs from each end of a rod that is balanced in the middle. The device enables you to conclude either that the contents of the dishes weigh the same or that the dish that falls lower has heavier contents than the other.
The 12 marbles appear to be identical. In fact, 11 of them are identical, and one is of a different weight. Your task is to identify the unusual marble and discard it. You are allowed to use the scales three times if you wish, but no more.

Note that the unusual marble may be heavier or lighter than the others. You are asked to both identify it and determine whether it is heavy or light.

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Logic Riddles 4 : Cross Bridge Puzzle
Difficulty ★★★★☆     Popularity ★★★★☆

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?

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Logic Riddles 5 : Popular Age Problem
Difficulty ★★★★☆     Popularity ★★★★★

Two old friends, Jack and Bill, meet after a long time.

Three kids
Jack: Hey, how are you man?
Bill: Not bad, got married and I have three kids now.
Jack: That’s awesome. How old are they?
Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date.
Jack: Cool… But I still don’t know.
Bill: My eldest kid just started taking piano lessons.
Jack: Oh now I get it.

How old are Bill’s kids?

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Last Updated:2011-10-14


  1. Puzzle num:1
    Answer is 3 airoplanes needed.All the 3 airoplane(say A, B and C) start together from the island in same direection and move till all of them get their 1/3 of fuel consumed.At this time, B gives 1/3 of its fuel to A and returns back to now,A has full tank, and C has 2/3 fuel left.Now again they mobe until, A is left with 5/6 of fuel and C is left with 1/2 of fuel.Now, C gives 1/6 of fuel to A and returns back.Now B comes back and picks C.Similarly , the other two planes B and C goes in oppsite dirction to bring the plane A

  2. Puzzle num:2
    10 ..Alternate solution.
    Arrange the bottles in the form of cube of dimension 10*10*10.
    Choose 10 prisners and make them drink bottles in all the three dimensional arranegement. Now,after 24 hrs see, who are the prisoner died, now, depending upon the intersectin value of their axes, you can find the bottle which has the poison in it.

  3. Divide the 12 coins into 3 parts, and number them 1,2 .....till 12.
    now group them as (1,2,3,4)=a , (5,6,7,8)=b and (9,10,11,12)=c
    if a=b, than errror is in c
    now group (9,10) and (1,2) measure

    if wt(9,10) > wt(1,2)
    error is in 9 or 10 and its heavier
    if 9>10, than 9 is odd,otherwise 10.
    if wt(9,10)=wt(1,2)
    error is in (11,12)

    compare 1 and 11, if 1=11, than 12 is odd, otherwise 11.
    similarly, we can find when wt(9,10)(5,6,7,8)
    replace 2,3 ,4 by 9,10,11
    and replace 5 by 2, and 6 by 12
    now, if (1,9,10,11)> (2,12,7,8)
    it means , error is in 1 or 7 or 8
    now weigh 1 & 7, if 1=7, than 8 otherwise 1 or 7 , whosoever is heavier than other.
    similarly , we can find in the other case.

  4. You can also do it this way. Lets say one marble is heavier than the other eleven. Divide it into two group of 6 marbles each and weigh them. One side will be heavier. Now divide the heavier side of 6 marbles equally and weigh it again. Now one side of 3 marbles with the odd marble will be heavier. Take those 3 marbles and weigh two of them, one on each side. If both are equal, then the 3rd marble is the odd one out, else one of them is heavier which is the culprit. Use the same logic if the odd marble is lighter than the rest.

  5. But how can we say earlier that marble is heavy or not

  6. Jack Robbins' assessment does not work. The first weighing does not tell you which side is heavy or light, therefor you will run out of weighing numbers before you have identified if the marble is heavy or light

  7. Marble problem answer by Vishwa - if odd ball is 11 or 12, then finding heavy or light require another weighing!