Brain Teasers 41 - Puzzle Prime

Cucumbers

Section: Brain Teasers Category: Mathematics

Difficulty: Medium

You had 10kg of cucumbers, each of which consisted of 99% water. After leaving them in the sun, some of the water in the cucumbers evaporated. If the cucumbers ended up with 98% water in them, how much of their weight did they lose?

SOLUTION

The cucumbers lost half of their weight.

If the water was 99% of the total weight, the remaining substance must have weighed 0.1kg. If after the evaporation the substance comprises 2% = 1/50 of the cucumbers, the total weight must be 50 x 0.1kg = 5kg.

Unknown Author February 17, 2019

20 Comments

FEATURED

Square Triangle Circle

Section: Brain Teasers Category: Insight

Difficulty: Medium Tags: Featured

Can you draw a 3-dimensional object which looks like a square when looked from one side, a triangle when looked from a second side, and a circle when looked from a third side?

SOLUTION

The object bellow satisfies the requirements.

Unknown Author February 9, 2019

3 Comments

FEATURED

Six Friends Camping

Section: Brain Teasers Category: Lateral

Difficulty: Advanced Tags: Featured

Monday, six friends went camping. Tuesday, John, Jack, and James cooked some mushrooms. Wednesday came and they ate the mushrooms. Thursday found them dead. Exactly one friend survived, how come?

SOLUTION

The six friends are called John, Jack, James, Tuesday, Wednesday, and Thursday. John, Jack, James, and Tuesday cooked the mushrooms. Wednesday joined them and they ate the mushrooms. Thursday was the one to find them dead, so he is the survivor.

Puzzle Prime February 5, 2019

2 Comments

Largest Matchsticks Number

Section: Brain Teasers Category: Insight

Difficulty: Advanced

Move just two matchsticks so that you get as large a number as possible.

SOLUTION

You can take the two horizontal matchsticks from the first 0, form the number 11 with them to get 11000¹¹. You can also make 11¹¹⁰⁰⁰ if you don’t mind that the power’s font is larger than the base’s font, or use the quite uncommon operation “tetration” to get ¹¹11000.

Source:

Puzzling StackExchange

bleh January 25, 2019

2 Comments

The Golden Cylinder

Section: Brain Teasers Category: Science

Difficulty: Advanced

You are shown two cylinders – one of them is made of gold and hollow, the other one is made of alloy and solid. Both of them have the same weight, shape, and are colored in black. How can you figure out which cylinder is the golden one, without scratching the paint?

SOLUTION

Simply roll the two cylinders on the ground. The hollow one will roll farther than the solid one since it will have a higher moment of inertia.

Unknown Author January 25, 2019

5 Comments

Dog on a Measuring Scale

Section: Brain Teasers Category: Insight

Difficulty: Easy

A dog is standing with three of its legs on a measuring scale, keeping its fourth leg in the air. If the scale is displaying 30lbs, how much will it display if the dog places its fourth leg on the scale?

SOLUTION

The answer is 30lbs since it does not matter whether the fourth leg is in the air or not.

Unknown Author January 22, 2019

0 Comments

Painting on the Wall

Section: Brain Teasers Category: Insight

Difficulty: Advanced

If you hang a painting over two nails on the wall and remove one of the nails, the string of the painting will stay over the other nail, and the painting will keep hanging. Can you wrap a string around the nails in such a way, so that after removing any of the nails, the painting will fall?

SOLUTION

The solution is shown below.

Unknown Author January 15, 2019

1 Comment

Spiders and a Fly

Section: Brain Teasers Category: Insight

Difficulty: Expert

There are a fly and three spiders on the edges of a cube. If the spiders’ velocities are at least 1/3 of the fly’s velocity, and all insects can travel only along the edges of the cube, show that the spiders can eventually catch the fly.

SOLUTION

Choose two opposite edges of the cube, then let two of the spiders “protect” them from the fly. You can do this by keeping the distance from the two spiders to the edges’ endpoints at most 1/3 of the distance from the fly to these endpoints. The remaining parts of the cube do not contain any loops, so the third spider can easily catch the fly there.

Unknown Author January 11, 2019

0 Comments

Two Barbers

Section: Brain Teasers Category: Lateral

Difficulty: Medium

There are only two barbers in one town. One of the barbers has a neat haircut and a clean working place. The other barber’s haircut is a total mess and his working place is dirty. Which barber would you choose to give you a haircut and why?

SOLUTION

You should choose the second barber. Since there are only two barbers, the chances are that they give each other haircuts. Also, probably the second barber’s salon is dirtier because he has lots of work and does not have time to clean up properly.

Unknown Author January 7, 2019

1 Comment