13 Stimulating Brain Teasers, Logic Questions, and Optical Illusions

Can you take on this tricky list of brain teasers, including riddles by Albert Einstein, without making a single mistake?

We've been in the lockdown for quite a while now, and if there's one thing we've learned for sure it's that working from home is a breeze with the right tools and that brain teasers and logic questions are a great way to ease our collective anxiety.

Here are 13 brain teasers, puzzles, logic questions, riddles, and optical illusions to help you while away the time. All of the questions come first, followed by the answers further down the article. Let's get started.

RELATED: 7 SIMPLE MATH EQUATIONS THAT WENT VIRAL AND DIVIDED THE INTERNET

1. Move just one matchstick

Here's an easy one to warm you up and get you started. Above is an equation, made out of matchsticks, that doesn't add up. Can you move just one matchstick to fix the equation? There's more than one possible answer. 

2. Three light bulbs and three switches

There are three switches downstairs. A devilish house planner made it so that these switches turn on three light bulbs in the attic. You can't see the lights when you are using the switches.

Each switch corresponds to one of the three light bulbs in the attic. You can turn the switches on and off and leave them in any position you like. 

How would you identify which switch corresponds to which bulb after going upstairs only once?

HINT: The picture might give you a little clue.

3. The three teacups conundrum

We've had a three light bulb brain teaser, so why not one about three teacups?

This brain teaser is taken from Henry Ernest Duduney's 1907 book 'Canterbury Puzzles', simplified by us into modern English.

A young lady at a dinner party, a Miss Charity, placed three empty teacups on a table and challenged anybody to put ten lumps of sugar in them so that there would be an odd number of lumps in every cup.

One young man at the party, who had been to Oxford University, and was studying law, passionately declared that, without a shadow of a doubt, it was not possible and that the proof was right there in front of them. 

It must have been interesting to see his face when Miss Charity revealed the correct answer. What was it?

4. A confusing math question

There are math questions that divide the internet, there are math questions that are impossible, and then there are math questions that seem impossible but really aren't. This is an example of the latter.

How is it possible for 8+8 to equal 4?

5. Which line is longer? 

A simple and straightforward question with a simple and straightforward answer.

6. Viral Facebook intelligence test

The following brain teaser is one of those famous viral IQ tests. It has been shared on Facebook more than 3 million times. Some people find it very easy while others struggle? Which group are you in?

• 6 + 4 = 210
• 9 + 2 = 711
• 8 + 5 = 313
• 5 + 2 = 37
• 7 + 6 = 113
• 9 + 8 = 117
• 10 + 6 = 416
• 15 + 3 = 1218
• ?? + ?? = 123

7. Einstein's riddle

The story goes that Albert Einstein created this riddle when he was young and that he predicted that only 2 percent of people would be able to get the answer. While there's no specific proof that he wrote it, it's an entertaining head-scratcher nonetheless.

Here’s the premise: There are five houses, each painted a different color. In each house lives a person with a different nationality. Each of the five owners drinks a certain type of beverage, smokes a certain brand of cigar, and owns a specific pet. None of the owners own the same kind of pet, smoke the same cigar brand, or drink the same beverage.

The question is: Who owns the fish?

Here are the clues:

• The Brit lives in the red house
• The Swede keeps dogs as pets
• The Dane drinks tea
• The green house is on the left of the white house
• The green house’s owner drinks coffee
• The person who smokes Pall Mall rears birds
• The owner of the yellow house smokes Dunhill
• The man living in the center house drinks milk
• The Norwegian lives in the first house
• The man who smokes blends lives next to the one who keeps cats
• The man who keeps horses lives next to the man who smokes Dunhill
• The owner who smokes BlueMaster drinks beer
• The German smokes Prince
• The Norwegian lives next to the blue house
• The man who smokes blend has a neighbor who drinks water

We recommend using a piece of paper to draw each house and make a chart for each category. This is a pretty tricky one.

8. A man in an elevator

A man lives on the tenth floor of his building. Every day, he takes the elevator down to the ground floor to go to work. When he gets back from work in the afternoon, he takes the elevator to the seventh floor and walks up the stairs the rest of the way to his tenth-floor apartment. He hates walking. Why does he do this?

HINT: There is nothing wrong with the elevator or the design of the building. It's a normal functioning elevator that goes to every floor.

9. Moving matches #2

For the sequel to the moving matches brain teaser you're allowed to move two matches. 

HINT: The digit of the number can be changed.

10. Life on Mars

Here's one we thought up ourselves here at IE.

You're suddenly transported to Mars by aliens. They've given you a spacesuit. One of the aliens asks you, what do you prefer?

You can spend five hours on Mars and we'll reveal to you the secrets of the universe. Or, you can spend a day on Mars and we'll tell you the secrets of the universe, and give you $5 million in any Earth currency.

In each scenario we will transport you back as soon as the time is up. For both scenarios we will give you exactly 24 hours of oxygen.

What do you decide? 

HINT: There is most definitely a right and a wrong answer.

11. A boy was playing with a book

A boy was playing with a book and tore out the pages 7, 8, 100, 101, 222, and 223. How many sheets did he tear out?

12. I am everything and nothing

Turn me on my side and I am everything. Split me in half and I am nothing. What am I?

13. Einstein's riddle #2

Here's another riddle that Einstein allegedly created.

Someone encounters a bear in a wasteland. There is nobody else there. Both the bear and the human were frightened and ran away from each other. Human to the north, bear to the west.

Suddenly, the person stopped, aimed their gun to the south, and shot the bear. What color was the bear?

HINT: If the bear ran about 3.14 times faster than the human (still westwards), he/she could have shot straight in front, however for the booty he would have to go to the south.

Answers

1. Move just one matchstick

5+4=9

0+4=4

8-4=4

2. Three light bulbs and three switches

The key is that light bulbs let off a noticeable amount of heat when they've been on for a while. So you can turn two bulbs on and wait for two minutes. Then, before going upstairs, switch one of the light bulbs off.

The one you switched off will be hot, the one you left on will be on, and the other switch's light bulb will be off and won't be hot.

3. The three teacups conundrum

Miss Charity had a trick up her sleeve. The illustration shows her answer. The numbers on the cups indicate the number of lumps that have been separately placed in each teacup.

By placing the cup that holds one lump inside the one that holds two lumps, it can be correctly stated that every cup contains an odd number of lumps. 

4. A confusing math question

8 a.m. plus 8 hours equals 4 p.m.

5. Which line is longer?

It's a trick question and an optical illusion — known as the vertical-horizontal illusion. Both lines are the same size as can be seen in the image above.

6. Viral Facebook intelligence test

Firstly, let's look at an example in the list of equations.

10 + 6 = 416.

How do you get 416 from those numbers?

10 – 6 = 4 and 10 + 4 = 16. If you write those two answers next to each other and you get 416. The other sums work in the same way.

So to get 123 you split it in two to get 1 and 23. See which numbers will add together to make 23. You also need to be able to subtract one from another to give you 1. 12 – 11 = 1 and 12 + 11 = 23. Write these together and you get 123, so the answer is 12 + 11 = 123.

7. Einstein's riddle

The owner of the fish is the German. For detailed charts and deductions on how to get the answer, have a look at this useful page by the University of Delaware.

8. A man in an elevator

The man is so small that he can easily reach the ground floor button, but he can only reach as high as the button for the seventh floor.

9. Moving matches #2

The answer is 51181.

10. Life on Mars

The correct answer is five hours and the secrets to the universe. A day on Mars lasts 25 hours. If you chose to stay a day with 24 hours of oxygen you would die from a lack of oxygen.

Have a look at this article to see an impressive visualization of the rotational speed of all the planets in our Solar System.

11. A boy was playing with a book

There are actually two possible answers to this riddle. Four or five sheets of paper.

The key to the answer is in the page numbers. At first glance, you’d think that three pages had been torn but it is not possible for page numbers to swap between odd-to-even and then even-to-odd. Whether it's four or five depends on the starting page of the book.

12. I am everything and nothing

The number eight. It looks like an infinity on its side and two zeros when split in half.

13. Einstein's riddle #2

For the human to have run north, and the bear west and to have still ended up south of the human, it all must have happened on the North Pole. So the bear will have been a white polar bear.