Riddle of the Sphynx
Which creature walks on four legs in the morning, two legs in the afternoon, and three legs in the evening?
SOLUTION
Man – four limbs as a toddler, two feet as an adult, two feet and a walking stick as an elderly.
Difficulty: Medium
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Bridge Over the River
Pinkbird is trying to get to Redbird across the river. Where should we place the bridge, so that the path between the two birds becomes as short as possible?
Remark: The bridge is exactly as long as the river is wide, and must be placed straight across it. Additionally, it has some positive width.
SOLUTION
Notice that no matter how the bridge gets placed over the river, the shortest path would be to go to its top left corner, then traverse it diagonally, then go from its bottom right corner to Redbird. The second part of the way has fixed length, so we must minimize the first part plus the third part. In order to do that, imagine we place the bridge, so that its top left corner is at the current position of Pinkbird – point A. If the bottom right corner ends up at point C, then we must connect C with the position of Redbird – point B, and wherever the line intersects the bottom shore – point D, that will be the best place for the bottom right corner of the bridge.
Mate in 1
White to move and mate in 1.
Remark: There is only one correct answer.
SOLUTION
The answer is Qa3#.
Unfaithful
Jack is looking at Anne, but Anne is looking at George. Jack is married, but George is not. Is a married person looking at an unmarried person?
- Yes
- No
- Cannot be determined
SOLUTION
The answer is YES. If Anne is unmarried, then Jack is married and is looking at an unmarried person. If not, then she is married and is looking at an unmarried person.
Move Move Chess
Consider a chess game in which every player is allowed to move twice per turn. Show that Black does not have a winning strategy.
SOLUTION
Assume Black has a winning strategy. Then if White plays Kb1-Kc3 and Kc3-b1 on his first turn, the game basically will start all over again, but with Black moving first. Therefore White will have a winning strategy, which is a contradiction.
10 Pounds of Flour
You have a big bag of flour, two 5lbs weights, and an inaccurate balance scale. How can you measure exactly 10lbs of flour?
SOLUTION
Put both weights on one side, then fill the other side with flour so that the scale balances out. Then remove the weights and replace them with flour so that the balance scale is balanced again. The amount of flour you put there is exactly 10lbs.
Vowels and Even Numbers
“If there is a vowel written on one side of a card, then there is an even number written on the other side.”
How many of these four cards do you need to flip in order to check the validity of this sentence?
What would the answer be if you know that each card contains one letter and one number?
SOLUTION
You need to flip all cards except for the second one. If each card contains one letter and one number, then you need to flip only A and 7.
FEATURED
Chicken, Cat, and Goat
What is 3/7 chicken, 2/3 cat, and a half goat?
SOLUTION
The answer is CHICAGO. CHI is 3/7 of CHICKEN, CA is 2/3 of CAT, GO is a half of GOAT.
Psychedelic Maze
Can you solve this psychedelic maze, created by Yonatan Frimer?
SOLUTION
The solution is shown below.
Alice in Wonderland
Get from START to FINISH in this maze, created by Joe Wos.
SOLUTION
The solution is shown below.
