This tag is meant for questions about the mathematical principles behind games, riddles, or their possible solutions. If the answer is known to you please do not use this tag to "riddle" other users, but rather to ask about the correctness of a possible solution or ways to extend and improve an ...

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3
votes
1answer
101 views

Magic Squares with Lucas and Fibonacci Numbers

I am quite curious about can we construct magic squares using only Lucas and Fibonacci numbers(of course not repeating them? If yes, how can we construct them? And if not , what is the proof?
1
vote
2answers
39 views

Arrangement of Numbers to Get a Common Sum

I'm having trouble with a math problem. I need to arrange 6 numbers on a certain diagram: At every intersection of two circles, I have to put one of these six numbers: 4, 5, 5, 6, 6, or 7. The sum ...
3
votes
1answer
145 views

Apparent paradox for the bird traveling between two trains puzzle

Gretings. Trying the "hard solution" for the puzzle below (which has been discussed, with a different angle, elsewhere on this forum) I got to a point where I have three seemingly valid solutions, ...
3
votes
1answer
35 views

is diffrence of raduis of 2 circles is not depend upon thier peremeter

I read on the Internet it's true, but I suspect it: Image describing the puzzle Take a ribbon tightly wound around the equator of the earth. Add 1 meter to that ribbon by cutting it at any ...
4
votes
1answer
63 views

Is there a way to divide an integer-sided square into integer-sided non-right triangles?

Integer-sided right triangles will fit into a square: but how about integer-sided non-right triangles? Here's a near miss - they don't quite fit like this: Is it possible?
0
votes
1answer
66 views

Demystify / Solve a number progression.

I've worked on this for two days and haven't gotten anywhere. They don't seem to grow by an even percentage, nor by an incremented percentage, nor by a flat number increment. (as far as my limited ...
6
votes
2answers
153 views

Regularities when $n$ and $2n$ contain the same digits

Suppose we would like to find positive integers $n$ such that the base-10 representations of $n$ and $2n$ contain precisely the same digits. $142857$ is a well-known example, and computer search ...
10
votes
1answer
406 views

Interview Question Asked In yahoo

Can you find the smallest positive number such that if you shuffle the digits of the number in a particular order, the shuffled number becomes twice the original number. Source: ...
0
votes
1answer
90 views

Help in figuring an optimum spider speed [closed]

When a spider threw its web at a fly then one end of the spider's web sticks to the fly and the other one to the table's surface. The fly immediately tries to pull away from the spider's web and ...
0
votes
3answers
97 views

Probability that a leap year has 52 Sundays

For the Question "Find the probability that a leap year has 53 Sundays". The Solution goes : For 53 Sundays, we proceed as: $\frac{366}{7} = 52.28$; So we can be sure that there are 52 Sundays, ...
1
vote
3answers
57 views

Find Differences between Ages of A and B.

Question: A says to B, I am twice as old as you were, when I was as old as you are. If the sum of ages is 63 years. Find the difference between their ages. My Question: I understand that we need to ...
0
votes
1answer
56 views

Liar - Truth-Sayer - Tourist Problem. Construct the answer with the given 2 sub-statements.

A tourist A comes to a country where people are divided into two categories: Liars (L) and Truth Sayers (T). Ls always lie and Ts always speak the truth. Intending to walk to the capital, the tourist ...
28
votes
4answers
542 views

Fibonacci numbers from $998999$

Is there a nice explanation of ...
0
votes
1answer
71 views

The famous Portia's casket problem

Gold casket: the portrait isn't in the silver casket. Silver: the portrait isn't in this casket. Lead: the portrait is in this casket. At least one of the statements was true and at least one of them ...
2
votes
1answer
63 views

Generating functions and the blue eyed daughters

There is a famous problem, given that a man has a number of daughters and if you were to meet two of them at random there is a 50% chance that both have blue eyes. How many daughters does the man ...
1
vote
0answers
68 views

Hanging a picture with Beta functions

There's a classic puzzle that goes something like this: You have two nails in a wall, and you want to hang a picture with a string (think of a necklace with a pendant) in such a way that if you ...
3
votes
4answers
417 views

A logic problem, which involves math

Imagine I'm walking in a tunnel and I stop, seeing that I am three eights of the way in. The tunnel is divided into eight equal length sections. All of a sudden, I hear the engine noise of a train ...
7
votes
3answers
356 views

No of comparisons to find 2nd smallest number?

you have 32 numbers. What is the least number of comparison needed to find the 2nd smallest out of them. As per me it 61 comparsisons are required. Compare first two number in list. Assign largest ...
12
votes
4answers
919 views

A logic problem. No need for calculation

Three people were told to go to a cave and each pick up a hat in pitch dark. The three then came out of the cave with the hat on their heads. There were five hats in the cave. Three of them are black, ...
1
vote
2answers
61 views

Stuffing envelopes

I've been trying to solve a following riddle A secretary types four letters to four people and addresses the four envelopes. If she inserts the letters at random, each in a different envelope, ...
1
vote
1answer
63 views

Calculating completed percentage of a jigsaw puzzle

At first I thought the solution for this problem was simple…maybe to you it will be, but it evades me at present. I need to figure out how to calculate the completed percentage of a jigsaw puzzle. ...
0
votes
1answer
55 views

What does this word represent?

What five digit number does serve represent if VCR+VCCT=SERVE? I have tried using 4,5,and 6 for C but that doesn't seem to work. Please help I do not understand.
-1
votes
3answers
379 views

Tricky Question with multiple solutions but only one true answer [closed]

If 1112=25 1113=36 1114=47 1115=58 1117=? I came up with two solutions 80 and 710 Which would be the right answer?? there is no further hints and there is only one a single solution answer
1
vote
1answer
67 views

Find the missing term?

...
1
vote
5answers
164 views

Algebra problem stumping me

I have recently run into an algebra problem that goes as follows. Using the digits $1$ to $9$, $$ \left\{ \begin{align} A + B + C + D &= EF \\ E + F + G + H &= CJ \\ B + G + J ...
0
votes
4answers
67 views

Island of knights and knaves

This question is about an island of knights and knaves, where knights always speak the truth and knaves always lie. You encounter two people A and B. Determine, if possible, what each of them are if ...
1
vote
1answer
52 views

Keys and key hole puzzle odds.

You have 13 keys... and 5 key holes.... 5 keys work in the 5 key holes... In random chance what are the odds of getting randomly all 5 keys in the right key holes on the first atempt. Bonus. ...
1
vote
1answer
34 views

Show that there exists a satisfactory assignment for the unstandard language of arithmetic $\{\textbf{0}, ', <_1\}$

Consider: $A1: \textbf{0} \not = x'$ $A2: x'=y' \rightarrow x = y$ $A3: \neg x < \textbf{0}$ $A4: x < y' \leftrightarrow (x < y \vee x = y)$ $A5: \textbf{0} < y ...
1
vote
2answers
99 views

Logic: Door to million dollars

You approach two doors. There are two men. Each man stands in front of one door. Through one door you will win one million dollars. Through the other they will take one million dollars off you. One ...
0
votes
1answer
24 views

Understanding a complex set description

I am trying to understand the following math expression, describing the possible sets of a 15 Puzzle: The expressions for tile and ...
4
votes
5answers
128 views

concerning a cheque

A man went into a bank to cash a check. In handling over the money the cashier, by mistake, gave him dollars for cents and cents for dollars. He pocketed the money without examining it and on the way ...
2
votes
2answers
89 views

Puzzle about convict who chooses length of his imprisonment

This is the puzzle I deal with for few days right now and I can't figure it out. I translated it from other language if I can improve post please comment. In the end of a trial judge sentenced a ...
1
vote
2answers
324 views

Maths brain teaser. Fifty minutes ago it was four times as many minutes past three o'clock

Fifty minutes ago it was four times as many minutes past three o'clock. How many minutes is it to six o'clock..? I have got the solution online but have doubts in it : ...
1
vote
1answer
73 views

Counting the number of cubes in an isometric view

I had seen questions in a sample aptitude test, where an isometric view of an object made up of cubes was given, with some of the cubes removed. We were supposed to count the number of cubes present ...
2
votes
2answers
78 views

Sudoku candidate probability

Supose a Sudoku puzzle row has four empty cells. The candidates for each cells is as follows: $3, 6, 9$ $7, 9$ $3, 6, 7$ $3, 7$ Looking at the possible cells for $3$ (cells $1$, $3$ and ...
1
vote
1answer
50 views

Independently rotating cubelets of a 2 x 2 rubiks cube?

I was reading up on 2 x 2 Rubik's cube. Wikipedia says that Any permutation of the eight corners is possible (8! positions), and seven of them can be independently rotated (37 positions). I ...
3
votes
6answers
238 views

What is the shortest way to write the number $1234567890$?

Here's a challenge : find the shortest way to write the number $1234567890$ . There is several ways to write the number $1234567890$ : $1.23456789 × 10^9$ $2×3^2×5×3607×3803$ $617283945×2$ But ...
1
vote
0answers
70 views

Number of paths in a grid

A common puzzle problem is to count the number of paths that start from the bottom-left-hand corner of a grid and end at the top-right hand corner, with the restriction that you can only move upwards ...
2
votes
2answers
143 views

Riddle about 3 men competing and never tying

Mr. A, B, C decided compete in athletics against each other. They competed in few disciplines. Winner got x points, second y ...
1
vote
1answer
46 views

Riddle about amusement park profit in relation to ticket's price

Price of the ticket at amusement park was cut down. In the result there was 50% more visitors in the park. At the same time profit from tickets' sale raised by 20%. What was the rebate for the ...
11
votes
11answers
1k views

A proportionality puzzle

My professor gave us this problem. In a foreign country, half of 5 is 3. Based on that same proportion, what's one-third of 10? I removed my try because it's wrong.
5
votes
2answers
83 views

Collection of numbers always in increasing or decreasing order

Anyone have any ideas on this question? I think you have to use the pigeon hole principle..but I am not sure about that? The numbers $1,2,3,\ldots,101$ are written down in a row in some order. Is ...
2
votes
2answers
48 views

Display Number as a sum so that sum of reciprocals of the summands is 1

Good Evening, Right now I am solving some Mathematic Puzzles and want to create a formula for the following: Display the Number 2008 as a sum of natural numbers so that the sum of the reciprocals of ...
1
vote
4answers
97 views

Move the last digit of $10k+9$ to the front, and obtain $70k+63$

"N" is a number and its last digit is 9. Delete the last digit (9) and write (9) to first digit, new number is 7 times "N". so whats that "N" ? Could anyone show me a way, how to solve such tasks? ...
0
votes
1answer
46 views

What is the legality of the following series?

What is the legality of the following series? 1,11,21,1211,111221,312211,132221,11133211,31231221,13111213112211,111331121113212221...
1
vote
0answers
53 views

Math Puzzle, finding a sequence with a certain property

A certain number of the $5000$ members of the Conway Mathematical Society (each of which has a different membership number between $1$ and $5000$) got together to discuss a puzzle. Much to their ...
3
votes
0answers
72 views

Given a number of items, how many sets of three are there where no two sets are two thirds similar?

Sorry if the title isn't proper math-talk. Hopefully I can explain it better here. So let's say we have a set. 1, 2, 3, 4, 5, 6, 7, 8, 9. I want to know how many groups of three can be made where no ...
12
votes
0answers
189 views

The Right Triangle Game

I am looking for a deeper understanding, particularly the optimum strategy and the maximum score as a function of grid size, of the following (single-player) game played with an $n$ by $m$ grid: ($6 ...
59
votes
12answers
13k views

Dividing 100% by 3 without any left

In mathematics, as far as I know, you can't divide 100% by 3 without having 0,1...% left. Imagine an apple which was cloned two times, so the other 2 are completely equal in 'quantity'. The totality ...
2
votes
1answer
37 views

Chord Maximisation

I am currently going back through all the "Challenge" questions in preparation for exams, and for this I do not know where or how to start, any hints would be appreciated. Now the way I have ...