BrainDen.com - Brain Teasers

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## Popular Content

Showing content with the highest reputation since 07/16/13 in all areas

1. 2 points

## A Simple Riddle

In our circles you may find A laugh, a wink, a grin But pressure us we'll likely snap And send away our kin. We don't do much, we go to pot Such simple ones are we But with your hand we take command Or from you we will flee.
2. 2 points

## Folding paper

Agree. When I hit the send button, I realized my thinking was too simple. But instead of deleting my post (moderator privilege) I left it to take its licks.
3. 2 points

## Simulating an n-sided die with two coins

Say we want to simulate an N sided die.
4. 2 points

5. 2 points

## Upside Down Cake

(This puzzle is from a blog called By Way Of Contradiction.) Imagine you have a circular cake, that is frosted on the top. You cut a d degree slice out of it, and then put it back, but rotated so that it is upside down. Now, d degrees of the cake have frosting on the bottom, while 360 minus d degrees have frosting on the top. Rotate the cake d degrees, take the next slice, and put it upside down. Now, assuming the d is less than 180, 2d degrees of the cake will have frosting on the bottom. If d is 60 degrees, then after you repeat this procedure, flipping a single slice and rotating 6 times, all the frosting will be on the bottom. If you repeat the procedure 12 times, all of the frosting will be back on the top of the cake. For what values of d does the cake eventually get back to having all the frosting on the top?
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8. 2 points

## I swear:

I swear: 1) To strangle the next person who uses 'suicide' as a verb. 2) That if I offended or hurt you in any way, I didn't mean it. 3) That I'll stop procrastinating. Tomorrow. Add whatever you swear.
9. 2 points

## Human origin" according to my own theory"

Personally, the original reason I believed in God is that an adult told me he existed when I was little and, being little, I took their word. But over time, I've listened to people talk about their experiences with God and seen it with others. I think I've seen Him get me through a lot of stuff the past few years that I don't think I'd have been able to make it through alone. You could say that I got through them because I worked hard, or just because believing in a higher power has some effect psychologically, or that there were coincidences involved, but when I put it all together, those reasons just don't work for me. But if I had to give just one reason that I believe God is real, it would be that He told me so. Audibly.
10. 2 points

11. 2 points

## Crazy People

eq ( 1 ) Study = not failed eq. ( 2 ) not study = failed add eq ( 1 ) & ( 2 ) study + not study = fail + not fail study ( 1 + not ) = fail ( 1 + not ) study = fail Then why should we study??
12. 2 points

## Blonde Jokes

this one is pretty cute! Blonde v.s. Lawyer a lawyer sitting on a plane next to a Blonde want to pass some time and turns to her and says, "how about a trivia game, if i ask you a question and you get it right I'll pay you 10 dollars, and if you get it wrong you pay me 1 dollar. then you ask me a question, with the same conditions." blonde says, "no thanks, I'm reading a book." the lawyer says, "okay how about this, 20 dollars for getting right for you, and 20 dollars for getting wrong for me." the blonde rolls her eyes and says fine. the lawyer asks, "whats the distance from the earth to the sun?" the blonde hands him a dollar. then the blonde asks him, "what goes uphill with 3 legs and down hill with 4?" the lawyer blinks for a second and says " i have no idea, i guess you win that round." then hands her 20. "okay my turn again, i am curious, what does go up hill with three legs and down hill with 4?" the blonde hands him another dollar.
13. 2 points

## One Up Me

What happens in quantum statistical thermodynamics stays in quantum statistical thermodynamics...b/c no one else cares.
14. 2 points

## One Up Me

Out of the frying pan and on to the floor. Back into the frying pan, let hope none of the guests saw.
15. 2 points

## Crocodile Sophism

I would think that the only way to make ANY sense of the situation is for the woman to repeat back to the croc EXACTLY what he said to HER: "If I guess right, you'll give my baby back, if I dont, you'll eat him. That's what you'll do to him." He'd have to return the baby, because she's CORRECT NO MATTER WHAT. Eh? hehehe
16. 1 point

17. 1 point

## 20 RIDDLES TO TEST YOUR MATH, IQ AND THINKING SKILLS.

. What is the value of x If 1/2, 2/3, 3/4, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10 then x/1000? x = 500,000 2. If 4 and 2= 26, 8 and 1 = 79 and 6 and 5 = 111. Then, what is 7and3?...410 3. What 3 positive numbers give the same result when multiplied and added together? 2 mis interpreted the Q 1,2,3 is correct 4. What number do you get when you multiply all of the numbers on a telephone's number pad? zero 5. Here is a light switch. Note the order of the positions. If the light is now at medium and it is switched 3922 times what will be the position of the switch? medium I assumed in the absence of additional info there were 3 positions . i.e low , med , high. any even number of flips will put the sw back on med 6. Can you arrange four nines to make it equal to 100. 99 9/9 8. If 1/2 of 5 is 3, then what is 1/3 of 10? 3.67 I envisioned 1/2 of 5 = 2 1/2 + 1/2 = 3; therefore 1/3 of 10 = 3.33 + 1/3 =3.367 9. 100 students entered college. 55 of them chose music. 44 of them chose sports. 20 of them chose both. How many of them chose neither music nor sports? 21 10. Four friends are going to a concert. When they arrive, there are only five seats together left in the theater. The manager will let all four friends in for free if one of them can tell her how many different seating arrangements are possible for four people with five empty seats. 120 5 seats taken 4 at a time 5 ! All four are let in free. Could you have given the correct answer? 120 5 seats taken 4 at a time 5 ! 12. At six oâ€™clock the wall clock struck 6 times. Checking with my watch, I noticed that the time between the first and last strokes was 30 seconds. How long will the clock take to strike 12 at midnight? 5 hrs 59 1/2 minutes 13. There are several books on a bookshelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf? 9 14. John has been hired to paint the numbers 1 through 100 on 100 apartments. my bad 20 How many times he has to paint 8? 20 15. You have two books. One of them is upside-down and the other is rotated so the top of the book is facing you. What is the sum of the first page in each book? 1 +1 16. There is a certain club which is for men only. There are 600 men who belong to this club and 5% of these men wear one earring. Of the other 95% membership, half wear two earrings and the other half wear none. How many earrings are being worn in this club? 600 17. Does a pound of gold or a pound of feathers weight more? feathers 18. There is a chain nailed to the wall. The chain is 10 feet long and the center of the chain dips down 5 feet from where each side of the chain is nailed to the wall. How far are the 2 ends of chain from each other? on the same nail 19.Little Johnny is walking home. He has \$300 he has to bring home to his mom. While he is walking a man stops him and gives him a chance to double his money. The man says "I'll give you \$600 if you can roll 1 die and get a 4 or above, you can roll 2 dice and get a 5 or 6 on at least one of them, or you can roll 3 dice and get a 6 on at least on die. If you don't I get your \$300." What does Johnny do to have the best chance of getting home with the money? keep on walking 20. If you have 6 women and 2 friends, how many women do each of your friends get if the friends are two of the 6 women;i.e. women themselves , then each is entitled to herself, or one each/ If the two friends are male then no women.
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20. 1 point

@SakuraChan
21. 1 point

PHASE
22. 1 point

## Connect the Dots

A little shorter then the obvious
23. 1 point

## logic sequences

Hi wiseabel, and welcome to the Den. So clearly there are several ways in which these numbers are similar and, equally clearly, we're to look for something beyond the fact they are integers. Three are odd, and a different group of three are prime. Three of the four contiguous pairs are descending. Only one of the digits (1) repeats among the numbers. At first glance, I don't see a common similarity, but I'll give it some more thought perhaps in a later post. Thanks for submitting a puzzle!
24. 1 point

## 3 remarkable numbers

I'll bet this is not the answer you're looking for, but it does qualify as a remarkable matchup:
25. 1 point

## rang the bell.

A man enter a room. In the room there is a 2 digits number on the wall. His friend outside the room do not know the number. But just by ring the bell once, his friend know the number. how could this happen ?
26. 1 point

## Rights Of Passage

and that led me to this..
27. 1 point

## Foreign Speakers

Can't find the page I was looking at. It had a list of cities that were part of the empire and the present country. Just looked at a map and it looks like Croatia was more Roman. May have been a few cities on the eastern border so that one was stretching it. I see you edited one
28. 1 point

## Spin the bottle (no kissing involved)

Based on this exacting 1000 time simulation of the best night of your high school life, you got very lucky!! BTW, this code works fine. from random import randint def he_gets_the_bottle(): if randint(0,9) == 1: return True def it_points_to_uma(): if randint(0, 9) == 1: return True def bonanova_gets_a_kiss(): if he_gets_the_bottle() and it_points_to_uma(): return True kisses = 0 for i in range(1000): if bonanova_gets_a_kiss(): kisses += 1 print kisses
29. 1 point

## Random bullets

Here is a simple puzzle using bullets fired at random speeds along a straight line. Every second, a gun shoots a bullet along a straight line.Each bullet has a random speed between 0 and 1. Bullets do not slow down; but if two bullets collide, both of them are annihilated.The gun stops shooting after 10 bullets have been fired.What is the probability that eventually all the bullets will be annihilated? Edit: BMAD previously asked if the bullets never stop firing, whether (at least) one bullet survive forever. It inspired a lot of debate, I think without resolution. This puzzle I think has a provable answer.
30. 1 point

For part I.
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32. 1 point

## Rats and cats

Two are playing the game "cats and rats" on the chess-board 8x8. The first has one piece -- a rat, the second -- several pieces -- cats. All the pieces have four available moves -- up, down, left, right -- to the neighbour field, but the rat can also escape from the board if it is on the boarder of the chess-board. If they appear on the same field -- the rat is eaten. The players move in turn, but the second can move all the cats in independent directions. a) Let there be two cats. The rat is on the interior field. Is it possible to put the cats on such a fields on the border that they will be able to catch the rat? b) Let there be three cats, but the rat moves twice during the first turn. Prove that the rat can escape.
33. 1 point

34. 1 point

## Friendly Mathematicians

At a certain mathematical conference, every pair of mathematicians are either friends or strangers. At mealtime, every participant eats in one of two large dining rooms. Each mathematician insists upon eating in a room which contains an even number of his or her friends. Prove that the number of ways that the mathematicians may be split between the two rooms is a power of two.
35. 1 point

## Marked Hat

36. 1 point

Pick three points on a plane at random (assume uniform probability density across the plane). What is the probability that the triangle so formed is obtuse angled? Source: general internet, with some slight changes. I got a surprising answer to this one..
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38. 1 point

## Sliding spheres

Of the two questions I asked, the first is the more elegant. The answer (contact angle) is the same for any size sphere or any planet. So long as the planet's mass is large compared to that of the sphere. The second question seemed reasonable to ask, and it surprised me a little that its answer (landing point) does depend on size and on gravitational pull. On Earth, the result shows that the apple does not fall far from the tree. I also heard someone remark that the angle (in degrees) is strikingly close to the answer to life and everything. See Hitch-hiker's guide to the galaxy.
39. 1 point

40. 1 point

## Red Queen

I googled this variant. It's called "Flying Kings" and it appears it only exists in international games (which are played on a 10x10 board) and certain "in house" rules. The one thing that seems common is that the King is only allowed to jump over 1 piece at a time (although it can continue in any diagonal direction once it's landed on a vacant square). i.e. it can't jump over 2 or more pieces that have no vacant square between them. Hope that clarifies
41. 1 point

## Posts and Titles

I have been poking around this forum for some answers to my questions, but I cannot find them. 1. What is the system for the number of things you post before advancing in a title? (Newbie, advanced, superior, etc.) 2. How many titles are there? 3. How are VIPs granted their title? 4. Where do "stars" come in on all this? 5. Do stars go 1-5 or only 1-4 or what? Please help me make sense of this system.
42. 1 point

## Masonry Chess

you can use the brown and grey tiles to represent the board and the red and yellow brick to represent each side, the "size" of the blocks together equal to its chess equivalent.
43. 1 point

## Fowl Play

Y-San, I think you are right.
44. 1 point

## One Up Me

(ghost) I never thought MiKi would do that to me for ticking her off!!!
45. 1 point

## Human origin" according to my own theory"

From what I've heard, in the original Hebrew of the Old Testament, the actual wording is a period of time, but that was translated to a "day." As to the rest of it. I am personally wary of evolution, and that's not because I'm religious but because I'm logical. I can see the earliest beginnings where the primordial soup formed the basics of life, and I can see the very end where evolution and natural selection are making subtle changes in species. However, I can't for the life of me see the middle. If you think about it, once you get even only to the first single-celled creatures, hardly any mutations will be beneficial. The chances are probably in the range of one out of a billion or so. That would mean you need billions of one species for a few to have beneficial mutations. Then the mutants have to be able to survive long enough to make a billion more of their kind, with many more, probably detrimental mutations getting in the way. While getting to the proper numbers probably wouldn't be a problem in the bacterial world, there is still a lot going against even them probability-wise. If you look deeper into the probabilities, you will realize that for every beneficial mutation, there will be millions of other mutations, most of them detrimental. The only way greater organization can come out of that is with incredibly large numbers. Again, this isn't much of a problem for bacteria, but when you carry this over to the multi-cellular world, I see major problems. Today we're worried about the genomes of species, including ourselves, degrading rather than continuing to evolve, for the same reasons that I just mentioned. So how could species have evolved so far up to this point, but only just now have genomic problems? I know some of it has to do with the lack of natural selection, especially in humans and agricultural breeds, but in no way does that cover all of it. The only solution I can come up with is divine intervention. Without it, I can't see any hope for complex life. So to get back to your theory, I believe all the species we're created by God through evolution. I don't think significant complexity-building evolution is possible without God. Some species may have evolved on their own, but from my observations, none of them are more complex than their ancestors. So maybe there was one race of mankind that other species diverged from, or maybe primitive man-like beings did evolve from apes, but I can't see equals to humans being the offspring of pure evolution.
46. 1 point

## Xxxx Rollo

as before - SHOPPERS = 0, SHOPPING = 1 so ?????ING = 1. so ANYTH??? = 0 from ANYTHING = 1. In APPETITE = 5 not A??????? from ANYTHING = 1, NOT ?P?????? from SPACEMAN = 0 so ??PETITE = 5 from 6. As SOLUTION = 1, TI <= 1 so ??PE??TE is proven. Maurice, I know you're reading this ya big galoot.
47. 1 point

## One Up Me

That would seem more impressive if we added a molten lava volcano to the end of every sentence, replacing the last word of the molten lava volcano.
48. 1 point

## The liar, the truth teller....and the random answerer

Have you found a solution, or are you just seeing what people come up with? I've thought about it and can't a way except this. Ask two men if they are men. You will definately ask the other man if he is (by other I mean the man that lies and tells the truth.) Since he can do both, I'm sure he'll yes yes. So will the truthteller. If on says no then you know who the liar is. If both say yes, then you still know who the liar is. Ask the liar if the first is the truthteller and the second is the liar (the first and second being the two that aren't the liar obviously.) If he says yes then it is the other way around. If he says no then you are right. Again, this is assuming that the man that can choose to tell the truth aor a lie will choose to tell teh truth and say he is a man. If he doesn't, then this could work, if you ask the right people. But, asking the right ones would be by chance and would not be reproducably effective.
49. 1 point

## Is it possible to give what we don't have?

Depends on what is meant by "have." [1] If have means "own," then yes. I can give someone something that I do not own. e.g. if I stole it. To give something, one only needs the ability to determine who controls it. If I control it, I can pass its control to someone else. So ... [2] If have means "possess the control of" then no. As stated, the paradox arises from the different antecedents of "with sorrow." Sorrow is the consequence of giving, not a possession before the act. But the language permits that interpretation by its form. Cute.
50. 1 point

## Hotel Bill

each person didn't pay \$9 because the total bill is \$25. \$2 was subtacted out of the equation unlike everything else was divided and multiplied. you can't multiply and divided and add and subtract in any order you want, do to order of operations. (PEMDAS)Perentases, exponents, multiply, divide, add, subtract. so remember to Please Excuse My Dear Aunt Sally.
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