Math and Logic Puzzles
May 9, 2020 Leave a comment
You are buying a roller on Amazon. Four similar rollers have the same functions, the 
same price, the same look, but different ratings.
Which product do you choose?
A. 8 positive ratings (8 total ratings)
B. 45 positive ratings (48 total ratings)
C. 90 positive ratings (98 total ratings)
D. 177 positive ratings (198 total ratings)
Find the answer at aplusclick.org.
April 5, 2020 Leave a comment
There are 5 counters in a bag. Three are Argentinean (blue) and two are Brazilian (green). Three counters are randomly picked out of the bag, one by one. They are not returned to the bag.
What probability is higher?
A. The probability of choosing three Argentinean counters in a row.
B. The probability of choosing two Brazilian counters in a row and then one Argentinean counter.
Find the answer.
March 1, 2020 Leave a comment
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.
February 16, 2020 Leave a comment
Seven secret agents are on payroll of a government.
Secret agent 001 spies on a secret agent who spies on secret agent 002,
who spies on a secret agent who spies on secret agent 003,
who spies on . . . spies on secret agent 007
who spies on a secret agent who spies on secret agent 001.
Who spies on secret agent 007?
January 13, 2020 Leave a comment
Gerry has several pets at home.
All of them are dogs, except for three.
All of them are cats, except for four.
All of them are tortoises, except for five.
How many dogs does he have?
December 1, 2019 Leave a comment
These are the Best Puzzles published at www.aplusclick.org in 2019.
October 6, 2019 Leave a comment
A 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
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?
July 12, 2019 1 Comment
How to choose the shortest road that connects several towns. This is a story about local and global minimums. Excellent presentation of soapy films.
May 27, 2019 Leave a comment
Leslie Green explains how our voting systems can be unrepresentative.
Five different parties are standing in an election for one representative. The voting methods: First past the post (FPTP): the party with the highest vote-count wins.
Is the voting system representative?
The no-pets party has 30% of the total, whereas parties that want pets are the remaining 70%. As it stands the FPTP system would vote-in the no-pets party, which does not represent the view of the electorate. What has happened is that the pro-pet movement has splintered, dividing the vote. In order to overcome this, one can use a transferable vote scheme so people can vote for their preferred option safely, preventing the hated no-pets party from winning.
A more detailed analysis can be found in an example.
