This puzzle is from "The Moscow Puzzles" by Boris Kodemsky is from another era - when there were things like clocks which need to be wound each day. If not they would stop. The puzzle goes like this.
I have a wall clock which is the only source for knowing the time in my house. One day I forgot to wind the clock and it stopped. Luckily, I have a friend whose clock shows the correct time always.
I walk down to his house, see the time in his clock, stay for a while and come back. Now I know the time and adjust my clock. It is is showing the correct time again.
How did I do that?
Answer: I wind up the clock before leaving the house and set it at 12 o'clock. It starts running. When I go to my friend's house I notice the time. And just before leaving the house, I also see the time.
When I come back, I see the time on my clock.
That will show the total time elapsed since I left home.
Now since I know the time in my friend's house as soon as I enter his house and just before I left his house, I know exactly how much time I spent there.
I subtract this time from the time elapsed. I get the total time walking to and from friend's house.
I divide it by 2. I get the time required to walk down from his house.
Now I can set the time on my clock as the time on my friend's clock while I was leaving his home plus the time I used to walk from his house.
Solution to puzzle 8: Maria is not counting Sundays. So she is not counting 1/7th of days of her age. That is to say she is only counting 6/7th of her age. 6/7th of her age = 30 Her actual age = 30 X 7/6 = 210/6 = 35 years. Puzzle 9 : The 4 coins problem You’re creating a new coin system for your country. You must use only four coin values and you must be able to create the values 1 through 10 using one coin at a minimum and two coins maximum. What 4 coins do you choose, and can you think of a second set of 4 coins that achieves the same goal?
Image from: Popular Mechanics By now you might have heard many, many, many puzzles of some people always telling truth, and others always telling lies. But in real life, we all neither knights, nor knaves. Anyway this puzzle is slightly different - there are couples and these couples both lie or both tell truth or one lies and other one tells truth. (We all like to believe ourselves to be the last one - wink wink) Dags, Eggs and Fens are being interrogated as one of them is a spy. One of the couples always tells truth. In another couple, both husband and wife always lie. And in the third couple, one of the spouses always lies and the other one always tells truth. Here are the statements by the three couples when interrogated. Mr. Dag: I am not the spy Mrs. Dag: Mr. Egg is the spy. Mr. Egg: Mr. Dag is truthful. Mrs. Egg: Mr. Fen is the spy. Mr. Fen: I am not the spy. Mrs. Fen: Mr. Dag is the spy. Which person is a spy? (This puzzle is take...
A scale is balanced. On one side of the scale, there are 3 1 ⁄ 2 bags of rice and on the other side there are 1 3 ⁄ 4 bags of rice and 1 ⁄ 4 kilo weight. What is the weight of one bag of rice? This puzzle is borrowed from the book "Brain teasers" by Ian Livingstone and Jamie Thomson Show answer Let the weight of 1 bag of rice be b. So 3 1 ⁄ 2 b = 1 3 ⁄ 4 b + 1 ⁄ 4 Transferring 1 3 ⁄ 4 b to LHS we get 1 3 ⁄ 4 b = 1 ⁄ 4 b = 1 ⁄ 4 / 1 3 ⁄ 4 = 1 ⁄ 7 kg
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