Open Us, Close Us
Open us, and you can’t see us without a mirror.
Close us, and you can’t see us at all. What are we?
SOLUTION
The answer is YOUR EYES.
Category: Brain Teasers
A collection of Riddle, Math, Chess, Detective, Lateral, Insight, Science, Practical, and Deduction puzzles, carefully curated by Puzzle Prime.
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6 Missing Letters
Fill the blanks with 6 different letters to read a meaningful sentence.
A _losopher of _sic in _na _ght about the _ances of _tch.
SOLUTION
You should add the 6 Greek letters φ (phi), μ (mu), χ (chi), τ (tau), ν (nu), π (pi), and get the sentence:
A philosopher of music in China taught about the nuances of pitch.
Clean Death
A man was going to bleach his socks because they had gotten muddy the day before. As he was pouring the bleach into the washing machine, he spilled some on the floor. He got some cleaning fluid and mopped it up with a rag. Minutes later he was dead. What killed him?
SOLUTION
When the ammonia (NH3), found in cleaning fluids, is mixed with bleach (a dilute solution of sodium hypochlorite, NaOCl), a deadly gas (monochloramine, NH2Cl) is produced that can kill a person instantly. The resulting chemical reactions are the following:
- Bleach decomposes, forming hydrochloric acid and subsequently chlorine gas:
NaOCl → NaOH + HOCl
HOCl → HCl + O
NaOCl + 2HCl → Cl2 + NaCl + H2O - The chlorine gas reacts with the sodium hypochlorite in the bleach, releasing chloramine as a vapor:
2NH3 + Cl2 → 2NH2Cl
Bicycle Tracks
You are chasing a criminal riding a bicycle, and you find his tracks left in the dirt. By investigating the tracks, can you determine which direction the criminal has fled to: left or right?
SOLUTION
The front wheels of the bicycle are traveling more distance and making sharper turns. Thus, the red tracks (as shown on the image below) correspond to the front wheel, and the green tracks correspond to the back wheel.
Then, since the back wheel is always pointing towards the front wheel, we conclude that the bicycle is moving towards the right.
Everything and Nothing
Turn me on my side and I am everything. Cut me in half and I am nothing. What am I?
SOLUTION
The answer is THE DIGIT 8.
If you turn it on its side, you will get the symbol infinity. If you cut it in half horizontally, you will get the number 0.
STANDARD Word
Given the word STANDARD, take away two letters and then add three digits to make a logical sequence.
SOLUTION
Remove the two letters A to get ST-ND-RD and then add the digits 1, 2, 3 to get 1ST-2ND-3RD.
Toasting Bread
Your toaster is broken, so you decide to toast your bread in a pan. The pan can hold three slices of bread at a time and takes 1 minute to toast one of their sides. How much time would it take you to toast four slices of bread on both sides using the pan?
SOLUTION
It would take you 2 minutes and 40 seconds. Label the slices with A, B, C, D, their top sides A1, B1, C1, D1, and their bottom sides A2, B2, C2, D2.
- Toast A1, B1, C1 for 40 seconds.
- Toast A2, B2, D1 for 40 seconds.
- Toast A1, C2, D2 for 20 seconds.
- Toast A2, C2, D2 for 20 seconds.
- Toast B1, C1, D1 for 20 seconds.
- Toast B2, C2, D2 for 20 seconds.
100 Guests in 99 Rooms
One hundred people entered a hotel that had 99 rooms, and each of them asked for their own room. In order to solve the problem, the bellboy did the following:
He asked the 100th guest to wait for a while with the 1st guest in room number 1, so that there were 2 guests inside. Then he took the 3rd guest to room number 2, the 4th guest to room number 3, and so on, until finally taking the 99th guest to room number 98. At the end he returned to room number 1 and took the 100th guest to room number 99, which was still vacant.
How could everybody get their own room?
SOLUTION
The two people who were taken to room number 1 were guest 1 and guest 100. Thus, the 2nd guest ended up without a room.