# All Questions

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### Multiples of their reversals

8712 and 9801 are the only 4-digit numbers which are multiples of their reversals: 8712 = 4*2178 and 9801 = 9*1089. Without using a calculator/computer, can you find two 5-digit numbers with this ...
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### Numbers that are the sum of the cubes of their digits

There are just four 3-digit numbers which are the sums of the cubes of their digits. For example: 370 = 3^3 + 7^3 + 0^3 and 371 = 3^3 + 7^3 + 1^3. Without using a calculator/computer, can you ...
169 views

### Mathematical golfing

You have probably heard of code golfing? There the task is to find the shortest computer program that produces the required output. Here we want to perform math golfing - find the shortest formula ...
66 views

### Find the missing shape

Here's a grid of shapes: Which of the following shapes should go in the missing cell, and why? There is only one correct answer, and the explanation should not be very complicated.
1k views

### Creating the hardest 10x10 maze

You are given an empty 10x10 grid. You are allowed to paint some of its cells as walls (black), while the remaining cells stay empty (white). A robot is programmed to start in the top-left corner of ...
172 views

### Move two matches (no [lateral-thinking])

Move two matches to make the following equation correct: Despite it commonly applying to puzzles of this kind, there is no [lateral-thinking] tag here, so no spelling out numbers, no turning the ...
83 views

### Assessment Centre Logic test

I have to exercises with solutions (red) from a german assesment centre logic test which I not understand: Does anybody the logic behind them?
130 views

### Complete this cross sequence

What is the next element of this sequence and why? Possible choices: Hint
52 views

### Can someone solve this sudoku without trial and error? Please explain

Stuck in this sudoku. If anyone can solve this then please share the method.
171 views
+300

### Scrambler puzzle (CTF forensics problem by me!)

Before anyone starts hyperventilating, this is not part of an ongoing CTF! I just made this example CTF problem for fun... To learn more about what a CTF is, check out this Wikipedia page. For this ...
84 views

### Find the equation of this surface - The Snowman

Here is a surface that resembles a snowman: Its equation has the form $f(x,y,z)=0$: if a point $(x,y,z)$ satisfies that equations it is shaded, otherwise it is "left blank". Your goal is to find $f$. ...
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### Cut It Up! (then find a phrase)

This is a "sorry for messing up yesterday's clues" puzzle. For each shape below, divide along grid-lines into identical pieces (rotation and reflection allowed). The first shape has 3 pieces, and the ...
61k views

### Cutting a cake into 8 pieces

Say, you are given a cake which you must share with 7 others. So, you must cut the cake into 8 pieces. But, you are only allowed to make 3 straight cuts. You cannot move pieces of the cake after the ...
90 views

### Tangential circles

The following figure has two axes of symmetry which define its width and length. The length (horizontal distance) is twice the width (vertical distance). The largest circle has a radius of 2005 and ...
6k views

### 9-5=5? Matchstick problem

Move one matchstick to make an equality. Question made by me (Is this too easy?)
824 views

### Hey, This is a 100th Puzzle of Mine!

Yep, this is my 100th puzzle here in PSE~ I'm really having a wonderful time here, thank you so much guys! >< I planned to write a harder and bigger one, but it turned out I was too lazy to do that....
479 views

### Slitherlink - It's all in the 2s

Can you solve this Slitherlink puzzle that I came up with? And in CSV: 3 - 3 - 2 - - 2 - 2 - 2 - - 1 1 2 2 1 - - 2 - 2 2 - - - 2 - 1 2 - - 1 - I tried to ...
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### What's the puzzle?

Someone sent me a photo of the last few lines of a puzzle. They were: BULLDOZER OVENPROOF BROADTAIL BREAKER ASYNTACTIC TIFF ALKYNE ABOUND EVASIVE BEVERAGE HILARITY COOTIE What ...
264 views

### Probability of picking the red marble twice

Start with a bag containing one red marble and one white marble. Reach into the bag and pull out a marble at random. Put it back and do it again. If, on both times, you grabbed the red marble, stop. ...
330 views

### Playing the Square Chess

On an ordinary chess board (8x8) without any pieces on it as a starting position, two players will alternately place a pawn on any square (unoccupied) so that the first player that form a square (...
4k views

### Creating the hardest 6x6 maze

You are given an empty 6x6 grid. You are allowed to paint some of its cells as walls (black), while the remaining cells stay empty (white). A robot is programmed to start in the top-left corner of the ...
1k views

Google cannot find me, reflected I'm lemon and lime, googling 'me' is when you fall, me and meme will answer all. What am I? Line 1 hint: Posted I still Line 2 hint: Take my reflection ...
510 views

### Boggling googling

I'm a number for you to evaluate, Googling 'me' gives the drop off the Empire State, Though the great Google finds no results for me, I'm just a pure integer value you'll see. What number am ...
143 views

### Cheapest strategy on average to find specific items in a set

The problem You have a set on N (around 15-30) seemingly-identical objects, which in fact comprises a small number D (unknown, between 1-3) of defective objects and the rest (N-D) are good. There ...
12k views

### What is the English word with the greatest number of consecutive repeated letters?

Example: one repeated letter - bitter two consecutive repeated letters - bassoon three consecutive repeated letters - bookkeeper I've tried to find a four-times-repeated example but failed. (...
921 views

### Random walking on a board

There’s a pawn starting in the center of this game board. At each move, it can advance randomly towards any of the adjacent squares sharing a common side with equal chance. What’s the probability of ...
You've to start with $1$ and can use each of the following operations at most once. You can do the following in any order you like: 1) Add $2$. 2) Add $3$. 3) Add $5$. 4) Multiply $2.$ 5) ...