## Aplusclick Best Puzzles 2019

December 1, 2019 Leave a comment

These are the Best Puzzles published at www.aplusclick.org in 2019.

Math and Logic Puzzles

December 1, 2019 Leave a comment

These are the Best Puzzles published at www.aplusclick.org in 2019.

August 20, 2019 Leave a comment

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.

In 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?

December 1, 2018 Leave a comment

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

January 1, 2018 Leave a comment

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?

Read more at

March 4, 2017 Leave a comment

*Mary has a cat, and a rat, and a hat, and a mat.*

**If the cat is on the mat, and rat is in the hat, but the hat is on the mat, where is the rat?**

This is a simple puzzle asked by Leslie Green, who collects dozens challenging puzzles. The collection of Leslie Logic and Math is presented at the website Aplusclick. It’s worth to try the challenging questions.

November 9, 2016 1 Comment

Math and Logic are full of paradoxes.

**1. Achilles and the Tortoise** The Paradox of Achilles and the Tortoise was described by the Greek philosopher **Zeno of Elea** in the 5th century BC. The great hero Achilles challenges a tortoise to a footrace. He agrees to give the tortoise a head start of 100m. When the race begins, Achilles starts running, so that by the time he has reached the 100m mark, the tortoise has only walked 10m. But by the time Achilles has reached the 110m mark, the tortoise has walked another 1m. By the time he has reached the 111m mark, the tortoise has walked another 0.1m, then 0.01m, then 0.001m, and so on. The tortoise always moves forwards while Achilles always plays catch up. Why is Achilles always behind the tortoise?

**2. Bermuda Triangle Paradox. **Why the sum of the interior angles of the Bermuda triangle is not 180 degrees?

**3. Simpson Paradox. **The average score for dance of boys and girls in class A are 16 and 21, respectively. The average score of boys and girls in class B are 15 and 20, respectively. Twenty percent of class A students are girls. Forty percent of class B students are girls. Which class has a higher average score?

**4. Braess paradox.** The diagram shows a road network. All cars drive in one direction from A to F. The numbers represent the maximum flow rate in vehicles per hour. Engineers want to construct a new road with a flow rate of 100 vehicles per hour. Drivers randomly choose the road at crossroads. What new road decreases the capacity of the network (the number of vehicles at point F)?

**5. Barber Paradox **In a city, the barber is the ‘one who shaves all those, and those only, who do not shave themselves.’

Who shaves the barber?

**6. The Two Envelope Paradox.** One envelope has twice as much money as the second one. Gerry does not know which envelope contains the larger amount. He takes one of the envelopes, counts the money, and is offered the chance to switch the envelope. He thinks “If the amount of money in the chosen envelope is X dollars, then the other envelope contains either 2X of 0.5X dollars, with equal probability of 0.5. The expected value of switching is 0.5 (2X) + 0.5 (0.5X) = 1.25X. This is greater than the value in the initially chosen envelope. It is better to switch.” What is your advice?

**7. Potato Paradox.** I have 100kg of potatoes, which are 99 percent water. I dry them until they are 98 percent water. How much do they weigh now?

**8. Leonard Euler’s Paradox. **Why the average of all of the numbers is not a zero?

1, -1, 2, -2, 3, -3, . . .

9. **Friendship Paradox. **Your friends have more friends than you. Why?

**10. Uninteresting Number Paradox. **How many uninteresting numbers exist?

**11. Gabriel’ Horn Paradox.** The shape obtained from rotating the equation about x-axis resembles a trumpet. If we need an infinite volume of paint to paint the infinite horn, how much paint does the horn can contain inside itself?

**12. Pop Quiz Paradox.** A teacher announces that there will be a quiz one day during the next week. The teacher gives the definition that they would not when they come in to the class that the quiz was going to be given that day. The brightest student says that the quiz cannot be on Friday because they will know the day. With the same technique, she eliminates Thursday, Wednesday, Tuesday, and Monday. “You cannot give us a pop quiz next week” she says. When does the teacher give the pop quiz? I know the paradox from Charles Carter Wald. Probably, Martin Gardner described it for the first time in The Colossal Book of Mathematics.

10. Uninteresting Number Paradox

May 2, 2016 Leave a comment

A **Bongard problem** is a kind of puzzle invented by the Soviet computer scientist Michael Bongard (1924–1971) in the mid-1960s. He died in 1971 during a hiking expedition in the Pamir Mountains. The tests played an important role in the disciplines of cognitive psychology and cognitive science. Human logical reasoning has a great advantage over computer intelligence.

**Be smart. Train your brain!**

Here several problems similar to the original Bongard problems go:

*What is the main difference between the pictures on the left page and on the right page? *

A.

B.

C.

Try to solve the problem yourself before looking for the answers in the A+Click Brainteaser Problems.

Harry Foundalis collected hundreds of Bongard problems.