The Best Aplusclick Puzzle 2020

Here they go


Chance for a Would-be Bride

girl-straws There was a tradition in old Russia. A would-be bride gathers six long pieces of straw and grasp them in her hand. She then randomly ties pairs of knots on the top and the bottom. Since there are six blades of grass sticking out above and below the hand, she will tie three knots on the top and three knots on the bottom. If she forms one big ring, she gets married soon.

Estimate the probability that the girl will get married soon.

The problem is mentioned in The New York Times NUMBERPLAY and it is credited to Sunil Singh.



vendormachineA drinks dispenser has three labelled buttons: JUICE, SODA, and LUCKY. If you press LUCKY you are supposed to get either juice or soda with equal probability.

Each button is wired to exactly one of these functions, but each function is not necessarily wired to exactly one button.

Assuming that you are clever, but unlucky, how many button presses are required to establish exactly which button does which function?


Check the answer

Back to School – Friendship Math

Group Of Children Sitting On Bench In Mall

It is the first day of a new school year, and this class has only 10 students.  Ashley has 9 friends, Betty has 8, Caleb has 7, Derek has 6, Elaine has 5, Graham has 4, Henri has 3, Ivana has 2, Julie has 1.  Name one of Fred’s friends.


friends4In a group of 4 school children, each child has exactly two friends, just one of which is their best friend. What is the minimum possible number of children for whom their best friend is also that friend’s best friend?



It is the first day of a new school year, and this class has only 10 students.  Ashley has 9 friends, Betty has 8, Caleb has 7, Derek has 6, Elaine has 5, Graham has 4, Henri has 3, Ivana has 2, Julie has 1.  How many friends does Fred have?


It is the first day of a new school year, and this class has only 5 students. Amy has no friends yet. Betty has one friend. Chris has three friends. Derek has two friends.  How many friends does Ellie have?


In a group of five students, Ann has one real friend among them, Betty has two,  Craig has three, and Dianna has two. How many real friends does Edgar have in the group?


18 Best Aplusclick Puzzles of 2018

New challenges:

What is the easiest way to make it correct?            Answer


In what Olympic sport does the winner cross the line facing backwards?      Answer


What time is it?         Answer


What is the necessary mirror size?     Answer


Find all 18 best puzzles at

A Self-educated Mathematician Established the Boolean Algebra


George Boole (1815–1864)

The term “Boolean algebra” honors George Boole (1815–1864), a self-educated English mathematician. Boolean algebra captures essential properties of both set operations and logic operations. Boolean logic is credited with laying the foundations for the information age (computers and cell phones).

One of the puzzles on Boolean logic:

There are three balls X, Y and Z. They are colored red, white and blue, but not necessarily in this order. One, but only one, of the following statements is true:

X is red

Y is not red

Z is not blue

3 balls
How many solutions does the puzzle have?

Think yourself before checking the solution.

Markov Chain in Every Day Life

The picture shows a subway map.  A team of inspectors verifies passengers’ tickets at a station on a line, or all lines through it if there are many lines.  Then they randomly choose the next neighboring station and move there to make their inspection.


Subway map

How many times higher is the probability of being inspected at station C than at station A?

Are you eager to know the answer? Try yourself before reading how Markov Chain helps to solve the problem. The answer is here.



The perfect explanation is given in the PBS Infinite Series video:

17 Best Puzzles of 2017


Aplusclcik team chose 17 Best Puzzles of 2017.

They are:

What country has the lowest birth rate in the World?


If certain words in this question are spelt wrong, how many of the eighteen words are spelt wrong?


A claustrophobic gentleman chooses his place in the train that will enter a tunnel just after the station. Where is the best place for him?2017Aplusclick3


Complex Problem Solving is Your Top Skill

Be ready for the Fourth Industrial Revolution!

According to the new World Economic Forum Report “The Future of Jobs” the most required skill is Complex Problem Solving together with Creativity and Critical Thinking.

Train yourself! Start with simple problems, for example, at Aplisclick, do it regularly and grow your most important skill.


Daan Roosegaarde uses technology and creative thinking to produce imaginative, earth-friendly designs and highlights the importance of the problem solving skills.

“There are no passengers on spaceship earth. We are all crew.” – Marshall McLuhan


Formula of Love

Professional dancersLove is like π – natural, irrational, and very important.” – Lisa Hoffman

Certain scientists think that love is a chemical state of mind and the formula for love is as follows:

dopamine + seratonin + oxytocin

C8H11NO2 + C10H12N2O + C43H66N12O12S2 

How many atoms  are there in the formula of love?