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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-2
votes
2answers
32 views

Find the missing dollar [duplicate]

Three friends eat at a restaurant and finally ask for the bill. They pay the 75 dollars by dividing it equally (so they spend 25 dollars per person.) The waiter takes the money to the owner, who, in ...
0
votes
0answers
57 views

Is there a general solution to the water-bucket logic problem?

Having an infinite supply of water and two containers, one for 3 liters and one for 5 liters, how would you measure 4 liters? Each step in the solution can be one of three things: Fill up a container ...
2
votes
1answer
33 views

Puzzle: Determining the structure of a bipartite graph

Consider the bipartite graph $G = (X, Y, E)$, with $|X| = |Y| = n$. We can think of $X$ and $Y$ as clusters of $n$ switches on either end of a long hallway. Each switch on one end of the hallway has ...
2
votes
1answer
69 views

A math puzzle about slow clock

You have the misfortune to own an unreliable clock. This one loses exactly 20 minutes every hour. It is now showing 4:00am and you know that is was correct at midnight, when you set it. The clock ...
-5
votes
4answers
130 views

Make $20$ using two “$3$”s [on hold]

By using two "3"s, how can we make $20$? We are allowed to use any mathematical sign.
1
vote
0answers
99 views

Maths puzzle 1: smart play with sets

Let $$X=\{ a, b, c, d, e, f, {ab}, {ac}, {ad}, {ae}, {af}, {bc}, {bd}, {be}, {bf}, {cd}, {ce}, {cf}, {de}, {df}, {ef}, {abc}, {abd}, {abe}, {abf}, {acd}, {ace}, {acf}, {ade}, {adf}, {aef}, {bcd}, ...
2
votes
1answer
28 views

Derive a formula for the number of small square base pyramids required to create a bigger pyramid?

To quote from the problem statement: "Pyramids are built using smallest pyramids of "level 1", that are used as building blocks for higher levels. Stacking pyramids of "level 1" to create ...
1
vote
0answers
35 views

Sum numbers game

$2n+1$ numbers are lined up as follows: $n$ , $n-1$ , $n-2$ , $\cdots$ , $2$ , $1$ , $2$ , $3$ , $\cdots$ , $n-1$ , $n$ At each step, one can choose any number in the line and add it to each of ...
14
votes
3answers
406 views
+200

Finding real money on a strange weighing device

You have 50 coins which each weigh either 20 grams or 10 grams. Each is labelled from 0 to 49 so you can tell the coins apart. You have one weighing device as well. At the first turn you can put as ...
0
votes
1answer
69 views

Can this expression be made true ? 2 _ _ _ _ = 2015

Make this expression true: 2 _ _ _ _= 2015 The underscores must be replaced by any 2 of of the operational symbols +, - , x, / (divide). And any 2 of the digits 0,1,2..9. So, you basically need 2 ...
2
votes
2answers
75 views

Probablity of $k$ balls go into at most (including) $m$ boxes, with $n$ given boxes ($m\le n\le k$)

Suppose I have $n$ boxes, and an infinity of balls. All balls are regarded the same. I randomly throw balls into the boxes, each time the ball may be thrown into one of the box, with equal ...
0
votes
0answers
10 views

Given An initial point and final point ,How to determine the number of Co-Ordinates(x,y) such that both x and y are integral?

I have thought a lot about it and still no clue. I thought of visualising the initial point and the end point in the form of a Grid. But ,soon I was over with my resources. Problem: Given an initial ...
0
votes
0answers
27 views

Right answer probability [duplicate]

I thought I'm familiar with probability, but this question got me a little stuck: If one choose an answer to this question completely random, the probability of choosing the right one is: A) ...
3
votes
1answer
83 views

Is my answer correct? Expected number of coin flips to get 5 consecutive heads

I found this puzzle online. Before my question gets flagged or on hold, I know the question has already been answered here but since I tried to solve it on my own I want to check if it's correct or ...
1
vote
1answer
55 views

Is there a mathematical way to determine a solution for puzzle games?

Or more specifically, a mathematical way to determine HOW to solve a puzzle game. Take a look at this screenshot of a puzzle game "The Talos Principle." As you can see, the purpose of this ...
3
votes
2answers
516 views

The sum of digits of $3(3x+3)$ is always $9$ for any $x$ between $1$ and $9$

Given the following 'joke' I stumbled across today It's easy enough to figure out that the answer is always 9. Asshole. However when I tried to 'prove' this for ...
5
votes
3answers
87 views

Number of ways through a modified grid

I was in math class listening to my teacher blather on about solids of revolution when my friend passed me a note with a puzzle on it. It looked something like this: How many different ways can you ...
0
votes
2answers
26 views

Aptitude: Time and Work

6 men can complete a piece of work in 12 days. 8 women can complete the same piece of work in 18 days, whereas 18 children can complete the piece of work in 10 days. 4 men, 12 women and 20 children ...
5
votes
2answers
128 views

A Knight and Knave Problem

There are $69$ people in a room, of which $42$ are truth-tellers (they always tell the truth) and the rest are liars (they can lie or tell the truth). You are allowed to ask any person $A$ whether ...
0
votes
1answer
31 views

Reasoning - Seating Arrangement

Eight fiends P, Q, R, S, T, V, W and Y are sitting around a square table in such a way that four of them sit at four corners of the square while the rest sit in the middle of each of the four sides. ...
5
votes
2answers
102 views

How to solve this riddle?

How to solve this riddle? All rooms have the same shape and size. Every room has one entrance, and two exits: one on the left, and one on the right (on opposite directions). Both exits lead to a ...
-4
votes
1answer
76 views

How do you make the number 43 using all of these numbers:7,7,6,5 [closed]

How do you make the number 43 using all of these numbers:7,7,6,5
0
votes
0answers
25 views

How many closed knight's tour are possible in a $8\times 8$ chessboard? [duplicate]

How many closed knight's tour are possible in a $8\times 8$ chessboard? I hae no such idea. Please give me the proof of it.
3
votes
1answer
93 views

Optimal strategy for 2 players Lights Out game variation

Consider a turn-based game for 2 players. They're both playing on the same board. The board is 8x8, randomly generated and each cell has 0 or 1 (with equal probabilities), for example: ...
3
votes
1answer
61 views

on which floor does she lives?

A woman lives in a 36 floor building. There is a lift in that building. When she leaves her aprtment and goes to lift,there are 3 times chances lift will take her up than take her ...
1
vote
1answer
67 views

Finding integer solution to solve a puzzle

I have been given the following puzzle: find the smallest number that it's right most digit is 2, and if you remove that digit and place it on the left most side of the number it will double its ...
3
votes
4answers
54 views

Sum of Digit Permutations

The question simply states "Let a secret three digit number be $cba$. If the sum of $cab + bac + bca + abc + acb = 2536$, what is $cba$?" I have no idea how to approach this problem. Any hints or help ...
18
votes
2answers
709 views

Puzzle: Cracking the safe [duplicate]

A safe is protected by a four-digit $(0-9)$ combination. The safe only considers the last four digits entered when deciding whether an input matches the passcode. For instance, if I enter the stream ...
1
vote
1answer
71 views

Min number of colors for shared light switches

I recently moved to a new house, and this house has more light switches than I'm used to. There a N lights in the house and M switches where N < M. A light may be controlled by 1 or more light ...
-2
votes
1answer
2k views

brain teaser that has me totally confused [closed]

A man stole \$50 from a shop owner. He came back and used the same \$50 to purchase a bread that cost \$40 and received \$10 change. How much money in all did the shop owner lose?
2
votes
1answer
31 views

Farthest Possible Distance for a Truck Fleet When Transferring Gas

Given a fleet of 50 trucks, each with a full fuel tank and a range of 100 miles, how far can you deliver a payload? You can transfer the payload from truck to truck, and you can transfer fuel ...
5
votes
3answers
97 views

100-Sided Dice “Blackjack” Game

I am attempting to determine two variables in this game: The optimum strategy: (What number the bettor should stay at) The expected value given perfect play: (The percent return on a bet when using ...
5
votes
3answers
84 views

Compass-and-Straightedge Construction

I stumbled upon this question in math class, and I got stuck. The Question: You're are given a circle, and two points. How do you construct a circle that goes through the two points and is tangent to ...
2
votes
1answer
94 views

How many triangles in picture? Formula or algorithm for this?

How many triangles are in this picture? Is there any formula or computer software to calculate this? Also: I know programming so I can program something to solve this if someone can point out an ...
0
votes
0answers
45 views

Weighing Coins Puzzle

Consider the following question: Suppose you have 8 coins. 3 of them weigh x units, 3 y units, 1 ...
1
vote
2answers
38 views

Alternate plain English algorithm for Towers of Hanoi

There are four plain English algorithms for the Towers of Hanoi Puzzle available on Wikipedia, but when I was first solving the puzzle, I came up with an algorithm that is different from any of the ...
6
votes
1answer
72 views

A runs 7/4 times as fast as B. If A gives B a start of 84m, how far must the winning post be…?

The problem statement in the book is: $A$ runs $7/4$ times as fast as $B$. If $A$ gives $B$ a start of $84$m, how far must the winning post be so that $A$ and $B$ might reach it at the same time? ...
1
vote
0answers
52 views

The minute hand of a clock overtakes the hour hand at intervals of 65 minutes of correct time. How much a day does the clock gain?

The question in the textbook is: The minute hand of a clock overtakes the hour hand at intervals of 65 minutes of correct time. How much a day does the clock gain? My method: The correct ...
3
votes
3answers
102 views

Puzzle: leaning a ladder at $45^\circ$ to a wall using only yourself

This question was asked to my friend in an interview. You are provided a ladder and are led to a wall. The ladder must be kept against the wall making an angle of $45^\circ$ with the floor. You are ...
1
vote
1answer
68 views

How many 3 digit even numbers can be formed by using digits 1,2,3,4,5,6,7 ,if no digits are repeated

How many 3 digit even numbers can be formed by using digits 1,2,3,4,5,6,7 ,if no digits are repeated ATTEMPT There are three places to be filled in _ _ _ I wrote like this _ _ 2 _ _ 4 _ _ 6 Now ...
0
votes
1answer
17 views

Distance and speed question on minimum time

Suppose that there is a narrow bridge 4 metres wide that only 1 bus can pass on it. The bus is travelling at 10m/s and it is moving with constant speed. A man is 2m away from the bus and is crossing ...
2
votes
1answer
40 views

Find the correct betting combination

Case 1: If we bet \$1 on team #1 and it wins then we will get \$2 Case 2: If we bet \$1 on team #2 and it wins then we will get \$4 Case 3: If we bet \$1 on team #3 and it wins then we will get \$6 ...
1
vote
1answer
71 views

Move a polygon to a specified position using only allowed rotations, reflections, and dilations

There is a puzzle in Recreational Math in Khan Academy which is very difficult to solve. This puzzle involves using a restricted amount of transformations. The question does not appear to work in the ...
2
votes
0answers
62 views

Has this puzzle got a name? [closed]

I really like this puzzle: https://www.youtube.com/watch?v=ud_frfkt1t0 Does it have a name? Has it been studied before? The question: Let $A$ and $B$ be independent and identical continuous random ...
6
votes
2answers
193 views

How many archers do I need to deploy to destroy an Archer Tower?

I was playing Clash of Clans and came across this interesting problem. Consider the case when I'm attacking an enemy war base with an Archer. My archer can cause a damage of 12 hitpoint per second. ...
2
votes
3answers
79 views

economist puzzle for

Mr. White and Mr. Black agreed on the plan to average the wealth by pairs of economic classes, but they differed on the order. Averaging means that the total wealth of the two classes is ...
2
votes
0answers
82 views

Math puzzle I have been stuck on

Have had this math puzzle that I have been unable to solve for a while. Each leter is a number between 1-9. No letter uses the same number twice (aka if B is 3 D can't be 3 also). The ? mark ...
2
votes
1answer
71 views

Difficult sequence puzzle

What is the 25$^{th}$ term of this infinite sequence? $$1,1,1,1,1,691,2,3617,...$$ I have tried for an hour now and I can't find any meaningful relation between the terms.
4
votes
4answers
751 views

A 3rd grade math problem: fill in blanks with numbers to obtain a valid equation

Even though this is a 3rd-grade math problem, people found it extremely hard. Any people have a solution, or algorithm is welcome. I'll try make a program base on the algorithm and see if it's ...
3
votes
2answers
31 views

Searching specific numbers based on clues

"Find x for 0≤x≤100,000." My clues are as following. I'm not sure whether there are multiple answers or that only one 'x' remains based on these clues: This number isn’t between 20,000 and 40,000 ...