Top 10 Logic Puzzles

So you think you are clever, right? Then here is your chance to pit your brain against some of the world’s hardest logic puzzles ever created.

1. 10 identical bottles of pills

We have 10 identical bottles of identical pills (each bottle contain hundred of pills). Out of 10 bottles 9 have 1 gram of pills but 1 bottle has pills of weight of 1.1 gram. Given a measurement scale, how would you find the heavy bottle? You can use the scale only once.

2. Camel and Banana Puzzle

The owner of a banana plantation has a camel. He wants to transport his 3000 bananas to the market, which is located after the desert. The distance between his banana plantation and the market is about 1000 kilometer. So he decided to take his camel to carry the bananas. The camel can carry at the maximum of 1000 bananas at a time, and it eats one banana for every kilometer it travels.

What is the most bananas you can bring over to your destination?

3. Measure 4 gallon of water from 3 gallon and 5 gallon water

How to measure exactly 4 gallon of water from 3 gallon and 5 gallon jars, Given, you have unlimited water supply from a running tap.

4. Pirates and 100 Gold Coins Puzzle

There are 5 pirates in a ship. Pirates have hierarchy C1, C2, C3, C4 and C5.C1 designation is the highest and C5 is the lowest. These pirates have three characteristics : a. Every pirate is so greedy that he can even take lives to make more money. b. Every pirate desperately wants to stay alive. c. They are all very intelligent.There are total 100 gold coins on the ship. The person with the highest designation on the deck is expected to make the distribution. If the majority on the deck does not agree to the distribution proposed, the highest designation pirate will be thrown out of the ship (or simply killed). The first priority of the pirates is to stay alive and second to maximize the gold they get. Pirate 5 devises a plan which he knows will be accepted for sure and will maximize his gold. What is his plan?

5. 2 Player and N Coin Puzzle

There are n coins in a line. (Assume n is even). Two players take turns to take a coin from one of the ends of the line until there are no more coins left. The player with the larger amount of money wins.

Would you rather go first or second? Does it matter?

Assume that you go first, describe an algorithm to compute the maximum amount of money you can win.

6. Secret Mail Problem

A wants to send a secret message to his friend B in the mail.
But C (A’s Friend), who A don’t trust, has access to all A’s mail. So A put his message in a box with a lock. But A is not allowed to send a key!

How can A send his message through securely?

7. Riding Against the Wind Puzzle

A horse rider went a mile in 5 minutes with the wind and returned in 7 minutes against the wind. How fast could he ride a mile if there was no wind?

8. Gold Bar Puzzle

You’ve got someone working for you for seven days and a gold bar to pay him. The gold bar is segmented into seven connected pieces. You must give them a piece of gold at the end of every day. What and where are the fewest number of cuts to the bar of gold that will allow you to pay him 1/7th each day?

9. 2 Eggs 100 Floors Puzzle

You are given 2 eggs. You have access to a 100 storey building. Eggs can be very hard or very fragile means it may break if dropped from the first floor or may not even break if dropped from 100 th floor.Both eggs are identical. You need to figure out the highest floor of a 100-storey building an egg can be dropped without breaking.
Now the question is how many drops you need to make. You are allowed to break 2 eggs in the process.

10. Grandma and Cake Puzzle

You are on your way to visit your Grandma, who lives at the end of the valley. It’s her anniversary, and you want to give her the cakes you’ve made. Between your house and her house, you have to cross 5 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake.

How many cakes do you have to leave home with to make sure that you arrive at Grandma’s with exactly 2 cakes?

32 Thoughts on “Top 10 Logic Puzzles

  1. PALANI on July 17, 2016 at 7:46 pm said:

    Take one pill from first bottle, 2 from second 3 from third and so on. If the weight is 55.1 its first bottle …

    • Gauntlet on July 22, 2016 at 3:10 pm said:

      10. Start backwards. You have 2 cakes after the 5th troll, it gave you one back after taking half, so 2*(2-1)=2 is the number of cakes you had before crossing the 5th bridge. The same thing will happen at every bridge thus you only have to bake 2 cakes as each troll will take 1 and promptly return it.

    • Utsav Pathak on February 6, 2017 at 9:39 pm said:

      Place all the bottles on the scale than one by one start removing the bottles and if the change in value of scale is 1.1 then it will be your answer

    • Utsav Pathak on February 6, 2017 at 9:41 pm said:

      Q-1 Place all the bottles on the scale than one by one start removing the bottles and if the change in value of scale is 1.1 then it will be your answer

  2. SasiRam on July 19, 2016 at 2:39 pm said:

    Q3. Fill 5 gallon jar with water and pour water into 3 gallon jar. 2 gallon of water will be available in 5 gallon. Now empty the water in 3 gallon jar and filled it by 2 gallon of water remained in 5 gallon. Then fill 5 gallon jar and pour water into 3 gallon jar, it will take 1 gallon to fill exactly, so the remaining 4 gallon will be in 5 gallon jar.

  3. Reddy on August 7, 2016 at 5:16 pm said:

    First take water in 5 gallon jar and pour in some vessel.then again take water in 5 gallon jar and pour in to vessel.now remove water with 3 gallon jar 2,times from the vessel .as there is already 10 gln water in the vessel ,after removing 6 glns( 2 times with 3gains) 4 gallons will be remaing

  4. first one is simple. take the scale place it over a bottle such that its equally balanced like weighing plane. then put 2 pill from each bottle on either end. which ever side bends that pill is heavier n so is the bottle :) :P

  5. srija Ekka on April 11, 2017 at 11:46 pm said:

    10-2cakes

  6. Prateek on July 13, 2017 at 4:32 am said:

    Ans 2….532 banana maximum

  7. Patrick Wooldridge on August 12, 2017 at 9:28 pm said:

    The first puzzle should be restated for clarity (current proposition has several ambiguities). E.g.,
    You have 10 bottles of pills, each containing one hundred pills. All the bottles look exactly the same and all the pills look exactly the same. Nine of the bottles contain pills weighing 1 gram each while 1 bottle has pills weighing 1.1 gram apiece. You have a measurement scale accurate to tenths of a gram, but you may use it only once. How can you find the bottle with the heavier pills?

  8. Creative on September 8, 2017 at 10:14 am said:

    500 banana
    1. Take 1000 upto 250 km and leave 500 banana there and return with 250 banana up to initial position.
    2. Take another 1000 banana upto 500 km and leave 250 banana there and return back 250 km with 250

    • Abhijeet Raj on July 10, 2018 at 7:52 pm said:

      Yes, Now, pick 250 banana out of 500 banana(as, no banana was left at 250 km landmark from start) left in that place and return to initial position with 250 banana.
      So, we have 250 banana at 250 km and 250 banana at 500 km.
      At last, take rest 1000 banana upto 250 km and take 250 banana with you,
      so that you have 1000 banana at 250 km and walk upto 500 km to collect 250 banana from 500 km.
      Now, you have 1000 banana and you have to travel 500 km.
      Thus, you left with 500 banana after completing your travel upto 1000 km.

      • Stephen Tellis on August 26, 2021 at 4:27 pm said:

        I can explain in a simpler way
        1)camel carries 1000 bananas from 0-250km 3times in which the camel consumes 1250 bananas. remaining=1750
        2)camel carries 1000 bananas once and 750 once. in which 750 bananas are consumed. remaining=1000
        3)camel carries the rest of 1000 bananas from 500-1000km and consumes 500 bananas.
        Thus, you are left with 500 bananas after completing your travel up to 1000 km

  9. sudipto on October 3, 2017 at 1:37 pm said:

    Ans 8
    3 cuts
    1 of size 1 another of 2 and last of 4….
    Frst day gve size 1
    Secnd day gve size 2 take back size 1
    Thrd day gve size 1
    Frth day gve size 4 n take back size 1 n 2
    Figth day give size 1
    Sixth day gve size 2 take back size 1
    Last day hve size 1

  10. Q3) Fill 5g beaker with water . Now pour this water in 3g of beaker . In end 2g of water will remain in 5g of beaker (5g-3g=2g) . Keep that 2g of water to a seprate place. Now empty both vessel and fill again 5g of vessel (as water tap is on ) , repeat the process . In end we will have 2g of water remaining . 2g + 2g = 4G of water !!!!!!!!!!!!

  11. ANILKUMAR GHIYA on November 27, 2017 at 10:42 am said:

    Q no 7 answer is 6 minutes for a mile.

  12. sachin gawde on December 9, 2017 at 2:15 pm said:

    0 banana

  13. Arnav Gupta on December 11, 2017 at 3:46 pm said:

    1) take n pills from the nth bottle and weigh. If weight comes to be 55.7 then its the 7th bottle, if weight come to be 55.4, then its the 4th bottle.
    2) 500 if we can assume that we can leave bananas in the middle of the desert.
    3) 5 to 3, 5 has 2 left, empty 3, pour 2 in 3, fill 5 and pour 1 to complete 3, the 5 has 4 liters left.
    4) 98,0,1,0,1- The logic is that if c1 dies, c2 gets most gold but c3,c5 wont get anything, so for c1 to swing the decision in his direction, he has to give c3 and c5 1 so that they vote for this theme.
    5) Did not understand the question :3
    6) Did not understand the question :3
    7) 10.28 miles/hour
    8) 3 cuts in the ratio of 1:2:4 – day one give 1, day 2 take 1 and give 2, day 3 give 1, day 4 take 1 and 2 give 4, day 5 give 1, day 6 take 1 give 2, day 7 give all.
    9)

    First thought which comes to our mind is to use binary search, we first drop Egg#1 from 50th floor, if it does not break, then try the middle of second half, if breaks then we have to try each floor in first half. But this will give worst case number of drops as 50(if it brakes on 50th floor, then we have to try from 1 to 49 floors sequentially).
    Second thought is to try xth floor then 2xth floor till 100th, in this case worst case time will be (100/x)+(x-1). worst case will be when Egg #1 breaks at 100th floor then we have to try Egg #2 from (100-x)th to 99th floors. In (100/x) + (x-1) equation, with increase in x, 100/x decreases while (x-1) increases, thus we can minimize it when 100/x = (x-1), this gives x ~10, which gives worst case number as 19 drops.

    But increasing the floor every time by x is not a very nice idea, as with each new increase in Egg #1 drop, we should decrease Egg #2 drops to minimize worst case number. so if we drop Egg #1 from xth floor initially, then in next turn we should try x + (x-1)th floor(to keep the worst case number same).
    Thus we can say X + (x-1) + (x-2)…1 = 100
    X(X+1)/2 = 100 => X=14.

    So we should drop Egg #1 from 14th, then 27th, then 39th and so on.
    10) 2 because 2/2 +1= 2. This was stupid :#

  14. Katlego on February 5, 2018 at 12:30 am said:

    Question 2

    For every 1 km a camel eats 1 banana, therefore 1000km = 1000 bananas

    Most bananas to bring at the market is Zero(0)

  15. Q:1 we can place all bottles at once and remove bottles one by one. In this way we can find the right bottle. Is it right?

  16. Chetan Singh on July 11, 2018 at 4:24 pm said:

    250 bananas: Take 1000 bananas to 250 kms leave 500 there, (500 bananas consumed by camel in travelling 250), do this two more times. In 2nd time camel consumes 250 bananas. Now total no of bananas are 1750(500+500+750), now from 250 kms camel had to travel 750 kms more and can carry upto 1000 bananas. So, the no of bananas left at 1000 km will be 250.

    • this works but leaves 750 bananas to rot in the desert at the 250km mark. So there was no point taking the camel back to collect the last 1000 bananas, should just set off after the 2nd 250km round trip with the 1000 bananas to reach the final destination with 250 but this still leaves 250 at 250km bananas in the desert to rot and 1000 bananas at the start to rot. There is a more effiecient way. take 1000 bananas to 400km consuming 800 (after going back) and leaving 200 twice to leave 400 at the 400km mark. the 3rd 1000 bananas the camel gets to 400km mark with 600 bananas and there is 400 waiting total 1000. take all 1000 bananas the last 600km which brings total of 400 bananas to market with none wasted.

  17. CHALAPATHI RAO KOMIRISETTI on August 10, 2018 at 9:50 pm said:

    Q.NO.3) Fill 3gallon jar with water then pour into 5gallon empty jar. Again pour 3gallon water jar into already filled 3gallon water of 5gallon jar but you can fill upto 5gallon of water in 5gallon jar so you left 1gallon water in 3gallon jar. Now empty the 5gallon jar then pour remaining 1gallon water in 3gallon jar into 5gallon jar. Now fill the 3gallon jar with water then pour into 5gallon jar ,now, we have 4gallon water in 5gallon jar

  18. Harish on October 9, 2018 at 8:04 pm said:

    First take watter in 5L bottle. Then fill the 3L into 3L bottle, then we have remaining 2 litters (5-3=2). Then again fill the five litter Bootle fill the 3litter bottle with one litre (bottle 1 alredy have 2 litters+ 1 from 5litter bottle =3) the remaining of 4 litter in 2nd bottle. We got exact 4 litters….

  19. Harish on October 9, 2018 at 8:15 pm said:

    First take water in 5L bottle. Then fill the 3 liters into 3L bottle, then we have remaining 2 liters (5-3=2) in 5L bottel.empty the 3L bottle then replace the 2 liters into 3L bottle.Then again fill the 5L Bootle and pour a water into the 3L bottle stop when it became a full. 3L bottle alredy have 2 liters + 1 from 5L bottle =3 and the remaining of 4 litter in 5L bottle. We got exact 4 litters….

  20. Harish on October 9, 2018 at 8:16 pm said:

    This is the correct answer: First take water in 5L bottle. Then fill the 3 liters into 3L bottle, then we have remaining 2 liters (5-3=2) in 5L bottel.empty the 3L bottle then replace the 2 liters into 3L bottle.Then again fill the 5L Bootle and pour a water into the 3L bottle stop when it became a full. 3L bottle alredy have 2 liters + 1 from 5L bottle =3 and the remaining of 4 litter in 5L bottle. We got exact 4 litters….

  21. Raunak on April 11, 2019 at 1:57 pm said:

    Q2 -0 banana

  22. Whatfor on April 26, 2019 at 10:00 pm said:

    5 it doesn’t matter if I should go first or second both have same result.
    N/2 is the algorithm to find the max. Amount of money

  23. Divyanshu Deo on August 3, 2019 at 10:03 am said:

    1 take 1 pill from 1st box ,2 pill from 2nd
    box …and 10 pill from 10th box and measure if it measures after decimal .1 then the heaviest is 1st box,if .2 then heaviest is 2nd box and so on

    2. 843 banana

    3 take one 3 gallon and two 5 gallon water and then remove three 3 gallon water

    7 six minutes

    10 two cakes

  24. Suzanne on August 18, 2019 at 4:41 am said:

    Q7: Rider with the wind
    Answer: Without wind he rides a mile in 6 minutes.
    The wind slows him down one minute if it’s against him (7minutes) and pushes him faster one minute if it’s with him (5minutes) .

  25. Amir Ata IRI on August 22, 2019 at 1:51 am said:

    The right way is to pit all bottles on thr scale and remove them one by one. If you remove a bottle(which contains pills of weight of 1g.) the total weigh will decrease by 100gram.(the total weight is 1010g).
    And if you remove the target bottle the weight decreades by 110 gram, thats the bottle which contains 100 pills of weight of 1.1 gram…

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