A variety of puzzles and brain teasers from physics, chemistry, math, and science. These puzzles will spice up your mind.
A farmer has 100 hens, numbered from 1 up to and including 100. Only the hens with the numbers 13 up to and including 48 each lay one egg. How many of the hens have not laid an egg?
(48 – 13) + 1 = 36 hens have laid an egg.
100 – 36 = 64 hens have not laid an egg.
There is a dish with three oranges. Suppose that you take two oranges from the dish. How many oranges do you have?
You take two oranges from the dish, so then you have two oranges.
Imagine you are on an island called Texel, with inhabitants that look the same from the outside, but differ in their truthfulness. We distinguish the following types:
Knights, who always tell the truth.
Knaves, who never tell the truth.
Normals, who sometimes tell the truth and sometimes lie.
Assume you meet one of these inhabitants, and he tells you: “I’m no Knight”. Then, of what type is inhabitant?
A Knight cannot make the statement “I’m no Knight”, since this would be a lie and a Knight always tells the truth. A Knave could also not make the statement, since that would be a true statement, and a Knave never tells the truth. A Normal however can say, “I’m no Knight”. It is true, and Normals sometimes.
A hunter leaves his cabin early in the morning and walks one mile due south. Here he sees a bear and starts chasing it for one mile due east before he is able to shoot the bear. After shooting the bear, he drags it one mile due north back to his cabin where he started that morning. What color is the bear?
He can walk one mile due south, then one mile due east and finally one mile due north where he finds his cabin again. This means that his cabin can only be at the North Pole, and for that reason the bear will be white.
Consider two cans, the first containing one liter of milk and the second containing one liter of water. Suppose you take one cup of milk out of the first can and pour it into the second can. After mixing, you take one cup of the mixture from the second can and pour it back into the first can. Which of the following statements holds now?
In the end, both cans contain again one liter of liquid each. So the amount of milk that is replaced by water in the first can (which is somewhat less than one cup!) equals the amount of water that is replaced by milk in the second can (it is just an equal exchange).
One day Alice meets the Lion and the Unicorn in the Forest of Forgetfulness. She knows that the Lion lies on Mondays, Tuesdays, and Wednesdays, and tells the truth on the other days of the week. The Unicorn, on the other hand, lies on Thursdays, Fridays, and Saturdays, but tells the truth on the other days of the week. Now they make the following statements to Alice:
Lion: Yesterday was one of my lying days.
Unicorn: Yesterday was one of my lying days too.
What day is it?
The only days the Lion can say that he lied on the previous day are Mondays and Thursdays. The only days the Unicorn can say this, are Thursdays and Sundays. Therefore, the only day they both say that is on Thursday.
A man is standing in front of a painting of a man, and he tells us the following: “Brothers and sisters have I none, but this man’s father is my father’s son”. Who is on the painting?
We can replace “my father’s son” by “myself” since he is the only child. Now remains: “This man’s father is myself”, so this man is his son.
It is dark in my bedroom and I want to get two socks of the same color from my drawer, which contains 24 red and 24 blue socks. How many socks do I have to take from the drawer to get at least two socks of the same color?
It is clear that taking zero, one, or two socks is not sufficient. However, if you take three socks, then either the first and second sock you take have the same color, or the third sock you take from the drawer has the same color as one of the previous two.