Questions tagged [mathematics]

A puzzle strongly related to mathematical facts and objects, or whose solution needs serious mathematical arguments. General mathematics questions are off-topic but can be asked on Mathematics Stack Exchange.

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2answers
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How many digits can be removed from a division puzzle?

Similarly to How many digits can be removed from a multiplication puzzle and still give only one answer? I am curious about division puzzles. I know this puzzle: . It has only 2 out of 42 digits $\...
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2answers
165 views

Standard Sudoku Specialized with just 2 Primes

A standard 9x9 Sudoku uses the digits 1 to 9. You are only allowed two distinct primes to represent 1 to 9. Find out the minimum number of characters (digits + signs) needed to construct a Sudoku ...
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2answers
281 views

Putting up the lights two

I hope you are familiar with this. Basically Each strand of 20 lights is wired like a 5x4 grid, and each bulb can be either blue, red, purple, or green. However, when you change the color of 1 ...
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8answers
4k views

How to use 2,0,1,8 to make 51? [closed]

How to use the number 2,0,1,8 to make 51? You can use any operation except for multiple factorials and you can concatenate numbers, ex.2,0=>20 You can take the square root of a number without a ...
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3answers
924 views

Crack the Code #3

You return to the bench after cracking the last code, and you notice an envelope on the ground directly under it. You put down your envelope with the previous code and pick up the new one, ...
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2answers
213 views

Arranging a long line of cards

Annie has a very long line of cards, numbered from 1 to $n$, such that every odd card is face-up and every even card is face-down. The only way she can modify the line is by taking any segment of ...
4
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1answer
702 views

Points on a cube

Professor Halfbrain has spent his entire weekend by placing colored dots on the surface of a huge wooden cube. His objective was to find large groups of dots that form the vertices of a regular ...
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2answers
986 views

Another 6 tries to guess a number between 1-100

Inspired by 6 Tries to Guess a Number Between 1-100, how many guesses would it take if you can ask if the outcome of an operation is equal, less than, or more than a number. In other words, Alice ...
4
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1answer
265 views

A Hollow Sphere

Imagine a sphere with a hole that has been drilled clean through its center (i.e. a cylindrical piece of the sphere is now missing). This new shape, with the core missing, has height of 6 when ...
4
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5answers
439 views

Determinant of Word Matrix

Challenge: Create a 3x3 matrix of letters (NO REPEATS) such that the determinant of the matrix forms words from the 'multiplications'. For example, in a simple 2x2 case, take the matrix $\begin{...
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2answers
380 views

5 weights on modified balance scale

This question is follow up version of What's the fewest weights you need to balance any weight from 0,5 to 40 pounds, on a modified balance scale with one arm twice as long as the other.   &...
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3answers
3k views

Solving a Rullo Puzzle

How can I solve in a (relatively easy) way, a Rullo puzzle? (Screenshot below) Rules: Enable or disable a circular number (pink is enabled) in order to make the row or column match the sum on the ...
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9answers
1k views

Make 6 5 4 3 = 1

Can you find a way to make: 6 5 4 3 = 1 by concatenation and/or adding any of (and only) these mathematical operators: + - × ! ÷ ^ standard parentheses () You cannot add other numbers to the ...
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2answers
1k views

Unique Licence Plates

Note: This is a Mathematical puzzle, not a Mathematical problem. Although the answer could be solved with mathematics, lots of problems on Puzzling SE could be solved with mathematics, and the problem ...
4
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2answers
505 views

Lock Optimisation

In a simple combination lock, a sequence of several digits is used as a password, with one wheel per digit. Generally, it is not possible to unlock the lock without knowing the password, but due to ...
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2answers
303 views

Alphametic with modulo

Solve this alphametic $ABCDEFG$ $mod$ $(A×B×C×D×E×F×G) = 0$ example : $ABCDE$ $mod$ $(A×B×C×D×E) = 0$ $13248$ $mod$ $(1×3×2×4×8) = 0$ Note : Do not replace any letter with 0. Each letter ...
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1answer
371 views

答えはまた二桁の数字、その3 (The answer is another two-digit number, #3)

A colleague at work gives you a slip of paper at work one day, with symbols written on it: ・のいろ・はおに・・ みほくへ・やしと・ち ・ま・り・・・・・ぬ ・るゑ・ひ・・を・け もわ・かせふ・よ・・ ・・こた・え・・・れ ・そ・・・・・つて・ あね・な・・・・さら ・・・...
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1answer
119 views

Keep the grid differences below $x$

Inspired by Keep the chessboard differences below eight Given an $n\times m$ grid of squares, what is the smallest possible integer bound $x$ for which it is possible to fill the squares with the ...
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2answers
668 views

Rotating teams through stations

How can 14 teams rotate through 7 stations (2 teams at a station) without overlaps? NOTE: Every team participates in every station exactly once
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1answer
220 views

Happy New Year?

Extend this infinite series by five more terms: 17, 3, 5, 7, 11, 17, 2, 3, 5, 11, 13, 17, 2, 5, 7, 11, 13, 2
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2answers
615 views

Does this strategy work?

I'm thinking about the following strategy for Fastest way to collect an arbitrary army: When a soldier decides to go to some house he "reserves" it. Once a soldier is free (has delivered the news to ...
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2answers
221 views

A final incident in the flea circus: Part 1

The ringmaster of a flea circus draws a square $ABCD$ with corners $A=(+1,+1)$, $B=(+1,-1)$, $C=(-1,+1)$, $D=(-1,-1)$ in the Euclidean plane and picks a point $P$ with integer coordinates outside ...
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1answer
161 views

Normal Knight sees the Big Picture during his Countrywide Travels [duplicate]

Normal Knight is savvy, energy saving as he travels through Regular Country... Ride along and Document Details of his Journey As this Knight (only chess move allowed) journeys through , he takes ...
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4answers
195 views

A curious incident in the flea circus

The ringmaster of a flea circus puts three fleas $A$, $B$, $C$ on three different numbers on the real number line, so that flea $B$ sits exactly in the middle between $A$ and $C$. Whenever the ...
3
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1answer
780 views

What movie am I?

The grid below contains the first part of a movie quote. What is the full 46-word quote, and what is the movie? Hint #1: Hint #2 Hint #3: Hint #4: Hint #5:
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1answer
237 views

Hackers have created a new scheme to send passwords

Note: Following puzzle was used in certain competition and every detail of task is virtual (This certain competition is not ongoing). Hackers have created a new scheme to send passwords. ...
3
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1answer
280 views

The game of pebbles +

The game of pebbles is a two-player game. The game starts with N stones. On a player's turn, he or she must remove either 1, a power of 2 (2,4,8,...) or a power of 3 stones (3,9,27,...). The player ...
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1answer
448 views

Black and white queens on an 8x8 chessboard

What is the largest number of queens that can be placed on a regular $8\times8$ chessboard, if the following rules are met: A queen can be either black or white, and there can be unequal numbers ...
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2answers
903 views

Game against the Devil

While browsing through S.E you notice a spider crawl right out from under your keyboard! Startled, you twitch your hand and left clicked your mouse. You look up in shock as you notice that you just ...
3
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1answer
267 views

Theoretical Question - Rubik's Cubes

I have a very basic question on Rubik's Cubes. Take any completely solved cube or skewb. Now pick out (with hand) any two similar pieces and swap their positions, without changing positions/...
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2answers
143 views

Three-digit multiplication puzzle, part II: ever heard of senary?

Followup to: Three-digit multiplication puzzle I'd never heard of "senary" either, until creating this series of three puzzles. It seems that "senary" is the word for base-six notation. Who knew? ...
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1answer
112 views

Deduce Distinct Digits of the Given Fibonacci Sequence- Detail all Steps

$DEPUS$ $SRST$ $UDQD$ $CTQU$ $DTPR$ $PQR$ $SDE$ $VRR$ $CVV$ $DUU$ $QP$ $TT$
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0answers
148 views

A partition of 79633 into thirteen parts [duplicate]

The sum of thirteen positive integers is 79633. If placed appropriately on the vertices of this graph, two of them will be joined by an edge if and only if they have a common divisor greater than 1 (...
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4answers
374 views

A sum and product from first principles

A question was put before Iron Man and Miss Tress. They were allowed to choose from the set $\mathbb{C}$ of complex numbers and asked to find a subset satisfying the conditions below: sum is zero ...
2
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5answers
634 views

Largest number with five 1's and five numeric operations [closed]

You have five 1's at your disposal, together with five arithmetic operations of your choice. However, as you only have five operations, you should choose them wisely. Question: What is the largest ...
2
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2answers
351 views

How to beat Count Dracula, part 2

This is a follow-up to "How to beat Count Dracula". Abraham Van Helsing and Jonathan Harker play a game against Count Dracula. The three players agree on the following rules: Count Dracula and ...
1
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1answer
254 views

Group trust problem [duplicate]

The previous part to this question is here. As a family generally has no more 5 kids, and I want to generalise the situation in the previous question, I shall change the context a little: There are ...
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3answers
551 views

How many chocolates?

One Christmas night, 3 kids were sleeping in their room. Their father came and kept a bag full of chocolates in the center of room with a card that says: "Sweets for my three sweet kids." At ...
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3answers
179 views

1984 - take the digits 1,9, 8 and 4 and make 369

Part II... Next year is the 70th anniversary of the publication of the book 1984 by George Orwell. Here is a puzzle to start the anniversary celebrations off a bit early ... Warm up Can you ...
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1answer
148 views

Professor Knowfair's triangle dissection assignment

Last Sunday I met with Professor Knowfair at the public library. We caught up and he told me about the most recent assignment he gave his students. He said: We had been studying medians and how ...
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3answers
2k views

Fair tournament for rotating teams of two

new to puzzles here. A real life situation led me to consider this. We have a small league of 6 people playing in teams of two. I would like to rotate the teams in such a way that everyone gets an ...
1
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1answer
213 views

Find the value of $\bigstar$: Puzzle 9 - Options

This puzzle replaces all numbers with other symbols. Your job, as the title suggests, is to find what value fits in the place of $\bigstar$. To get the basic idea down, I recommend you solve Puzzle 1 ...
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1answer
136 views

Combinations of pentagons on a 3 by 3 dot grid - how to use Burnside's lemma?

In the accepted answer to How many different pentagons in this grid?, Jaap Scherphuis says: After reducing for symmetry, only 23 are left, which you can check using Burnside's lemma. How did they ...
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2answers
238 views

The Number Kidnapper

I was just walking around with my friends Derek, Alice, and Peter, when suddely, WE WERE KIDNAPPED! We were driven away in a van to a secret hideout, where we met our kidnapper. He calls himself ...
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1answer
194 views

Fastest Way To 6 Pawns On the B To H Files

MASSIVE UPDATE: I decided to play around with this again today, and I found MAJOR improvmemts for the B to G file games. See if you can beat me! If not, give proof as to why my game is optimal (To ...
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5answers
262 views

How to get the sum 30 by choosing 3 numbers from these sequence? [duplicate]

I have a sequence of numbers - 1,3,5,7,9,11,13,15 I want to get the sum 30 by choosing 3 numbers from this sequence of numbers . The numbers can be repeated. Thank you
0
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1answer
123 views

The Chain Smokers [duplicate]

The Chain Smokers in our neighborhood are revered for their magical ability. They can use five cigarette butts to make a full cigarette. One day, they collected a 1000 cigarette butts. How many ...
0
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1answer
259 views

Possible numeric codes

This is a question I saw and solved a long time ago, it involves some maths. There is a keypad 1 2 3 4 5 6 7 8 9 A certain password starts with a 3. Each digit is adjacent (...
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2answers
242 views

Robbers - The ultimate compass challenge [closed]

Please read the Cops post for all details. Points are scored on the basis of how long a challenge remains unsolved before you solve. You may solve any number of challenges. You cannot solve your own ...
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1answer
188 views

Can you find this abundant dad and his six prime sons?

We are six little prime brothers. All our ages add up to the age of our abundant and old dad who is obviously not in his prime. However, if you pair him up with either of the prime neighbors, they ...