2,066 Medium Riddles With Answers - page 20 of 21
People have stepped on me, but not many. I never stay full for long. I have a dark side. What am I?
Very few people have literally stepped on the moon, it cycles through phases, and it has a permanently unseen far side.
My first four letters describe all living things. My last five letters are another word for knight. My job is to save you, and I'm a fan of water. Who am I?
"Life" (first four letters) covers all living things, and "guard" (last five) is a protector like a knight; a lifeguard saves swimmers by the water.
What falls but doesn't break, and what breaks but doesn't fall?
Night "falls" without shattering, while day "breaks" at dawn without literally falling.
Lovely and round, I shine with pale light, grown in the darkness, a lady's delight. What am I?
Pearls form in darkness inside oysters, have a pale glow, and are round jewelry pieces prized by women.
I'm like a doll, but I'm not for playing; I stand up straight, but if windy I may be laying; I'm well-known and famous for having no brain; I work outside both day and night in sunshine or in rain. What am I?
Scarecrows are stuffed figures that stand in fields, can topple in wind, and famously "have no brain."
A little pool with two layers of wall around it. One white and soft and the other dark and hard, amidst a light brown grassy lawn with an outline of green grass. What am I?
The "pool" is coconut water inside, wrapped by soft white flesh and a hard dark shell, sitting on husk-colored fibers.
I was carried into a dark room, and set on fire. I wept, and then my head was cut off. What am I?
A candle is lit ('set on fire') in a dark room, its wax 'weeps' as it melts, and its wick is eventually snuffed out ('cut off') at the top.
How many vertebrae in the human spine?
The spine consists of 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae.
First vaccine developed for which disease?
Edward Jenner used cowpox to immunize against smallpox in 1796.
What does the gallbladder secrete?
Bile is produced by the liver and stored/concentrated in the gallbladder.
How long is the large intestine?
The large intestine is wider but much shorter than the small intestine (which is ~20ft).
How many taste buds are on the tongue?
Taste buds are located in the papillae of the tongue and decrease as you age.
How many skin cells shed every minute?
Humans shed their entire outer layer of skin every 2-4 weeks.
What is the heaviest internal organ?
The liver is the largest and heaviest internal organ, weighing about 3-3.5 lbs.
Who created the first polio vaccines?
Salk developed the inactivated virus vaccine; Sabin developed the oral attenuated one.
How much blood is in the human body?
Blood volume is roughly 7-8% of total body weight.
World’s largest Hydroelectric Power Plant?
The Three Gorges Dam in China has the world's largest installed capacity.
What is the deepest part of the ocean?
Challenger Deep is about 10,935 meters (35,876 ft) deep.
How much water do Americans use daily?
The average American uses 80-100 gallons per day, but indoor use is around 50.
What provides 90% of atmospheric water?
Evaporation is the primary way water moves from the surface to the atmosphere.
How much of Earth’s water is saltwater?
Less than 4% of Earth's total water is fresh; the rest is saline.
Where is most freshwater located?
Over 68 percent of the world's fresh water is locked up in ice and glaciers.
How much water is stored in oceans?
About 96.5 percent of all Earth's water is held in the oceans as saltwater.
How many bones are in a giraffe’s neck?
Like humans and most mammals, giraffes have only seven cervical vertebrae, but they are very large.
What do you call a group of flamingos?
A group of flamingos is called a 'flamboyance' because of their bright colors.
How long can beavers hold their breath?
Beavers have physiological adaptations that allow them to stay submerged for long periods.
What are sea monkeys?
Sea-Monkeys are a hybrid breed of brine shrimp sold as novelty aquarium pets.
What animal kills the most humans each year?
Mosquitoes kill over 700,000 people annually by spreading diseases like malaria.
Largest mammal in North America?
The American Bison can weigh up to 2,000 pounds and stand 6 feet tall.
Which animal did Australia go to “war” with?
The Great Emu War of 1932 was a nuisance wildlife management military operation in Australia.
Average distance between Earth and the moon?
The average distance is ~384,400 km or 238,855 miles.
Where does the asteroid belt lie?
The belt is located between the orbits of the inner rocky planets and the outer gas giants.
Who was the first American woman in space?
Sally Ride became the first US woman in space in 1983 on the STS-7 mission.
How long for the ISS to orbit the Earth?
The ISS travels at 17,500 mph, completing about 15.5 orbits per day.
What is the coldest planet in our solar system?
Uranus has the coldest atmosphere, with temperatures reaching as low as -224°C.
When was our solar system formed?
It formed from a giant interstellar molecular cloud about 4.6 Gya.
Which two planets have no moons?
The inner-most planets, Mercury and Venus, are the only ones without natural satellites.
What is the hottest planet in our solar system?
Venus's thick CO2 atmosphere creates a runaway greenhouse effect, reaching 464°C.
What color is the sunset on Mars?
Dust in the Martian atmosphere scatters blue light more effectively near the sun.
Atoms with different masses but same element?
Isotopes have the same number of protons but different numbers of neutrons.
Element named after "greenish-yellow"?
Chlorine comes from the Greek 'chloros', meaning pale green.
Particles that make up protons and neutrons?
Quarks are elementary particles that combine to form composite particles called hadrons.
What are helium, neon, and argon called?
Noble gases are inert because they have a full outer shell of electrons.
At what temp are Celsius and Fahrenheit equal?
At -40 degrees, both temperature scales intersect and read the same value.
What is the newest element on the periodic table?
Oganesson (118) was officially named in 2016, completing the 7th row.
Most abundant element in the Earth’s crust?
Oxygen accounts for about 46% of the Earth's crust by weight.
What is a solid changing directly into a gas called?
Sublimation occurs when a substance skips the liquid phase (e.g., dry ice).
What scale measures the hardness of minerals?
The Mohs scale ranks minerals from 1 (talc) to 10 (diamond).
What is the splitting of atomic nuclei called?
Nuclear fission releases a huge amount of energy by splitting heavy atoms.
What is the red pigment that transports oxygen?
Hemoglobin in red blood cells binds to oxygen to transport it through the body.
How long is the memory of a goldfish?
Studies show goldfish can remember things for months, debunking the 3-second myth.
Which is the only rock that floats?
Pumice is a volcanic rock full of air bubbles, giving it a density lower than water.
How long does sun light take to reach Earth?
Light travels at ~300,000 km/s; the Sun is ~150 million km away.
What is the largest desert in the world?
A desert is defined by low precipitation; Antarctica is the world's largest cold desert.
What does a Geiger counter measure?
Geiger counters detect ionizing radiation like alpha, beta, and gamma rays.
How many bones do sharks have?
Sharks have skeletons made entirely of cartilage, not bone.
What element did Joseph Priestley discover in 1774?
Priestley isolated oxygen by heating mercuric oxide.
What is the study of fungi called?
Mycology is the branch of biology concerned with the study of fungi.
If you hammer a nail into a tree, where is it 5 years later?
Trees grow from the top (apical meristems), so a nail in the trunk stays at the same height.
What goes around the wood but never goes into the wood?
The bark is the outermost layer that surrounds the trunk but doesn't enter the interior wood.
What is neither water nor land but is always soaking wet?
Wetlands are areas where water covers the soil, creating a unique, soggy ecosystem.
Which element is derived from a Norse god?
Thorium is named after Thor, the Norse god of thunder.
What chemical doesn't like to follow?
A pun: 'Lead' is a metal, but the word 'lead' also means to be at the front or guide others.
I am the equivalent of a one-way street in the universe. What am I?
Time only moves in one direction�forward�according to the second law of thermodynamics.
You can't see me but I can see you. I can see right through.
X-rays have high energy and can pass through soft tissues but not bones, making them useful for imaging.
It is very hard to create me, but I can't be destroyed. I can only change form.
The Law of Conservation of Energy states energy cannot be created or destroyed.
I can be hot, cold, hard, and go through anything. What am I?
Water can be steam (hot), ice (hard/cold), and flow through various substances.
You can't see me, I can't be touched... but I cook your lunch. What am I?
Microwaves are electromagnetic waves that vibrate water molecules to generate heat.
When liquid splashes me, none seeps through; when I am hit, I change color. What am I?
Skin is waterproof and bruises (changes color) when struck or injured.
I am a ball that can be rolled, but never bounced or thrown. What am I?
An eyeball is spherical and rotates (rolls) in the socket but cannot be bounced.
Your mom and dad each gave you 23 of these threadlike strands. What are they?
Humans have 23 pairs of chromosomes, one set from each parent.
I can be good for you, but I can also be bad for you, and you will find me wherever you go. What am I?
Bacteria exist everywhere; some are beneficial (probiotics) while others cause disease.
I am under your face and outside your mind. What am I?
The skull protects the brain (mind) and is located beneath the facial features.
Rule: Circle=Yellow. Cards: C, S, Y, R. Check?
You check the Circle (to see if back is Yellow) and the Red card (to see if front is a Circle, which would break the rule). Yellow and Square can't invalidate the rule.
Pays payout in Yen. Charge to play?
The expected value is the average of all outcomes: (1+2+3+4+5+6)/6 = 21/6 = 3.5. To make a profit, the 'house' must charge more than the expected payout.
10 pennies in 3 cups, each has odd number.
Put 1 in the first, 1 in the second, and 8 in the third... but wait, the trick is nesting. Put 1 in cup A, 2 in cup B, and nest B inside cup C (which has 7). Now C has 9 (odd).
Spoon tea into coffee, mix, spoon back. More what?
Since you started and ended with the same volume in each cup, any 'tea' that stayed in the coffee must have been replaced by an exactly equal volume of 'coffee' in the tea.
Max slices from 4 straight cuts?
The formula is (n^2 + n + 2) / 2. For n=4, that is (16 + 4 + 2) / 2 = 11. This assumes cuts can overlap and pass through previous cuts.
Ways to arrange 8 books on a shelf?
The number of permutations is n factorial (n!). For 8 books, it is 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 = 40,320.
Monkey climbs rope with matching weight. Weight?
The force the monkey exerts to climb increases the tension in the rope equally on both sides. Thus, both the monkey and the counterweight accelerate upward together.
Reverses left/right but not up/down?
If you point your finger to the right, the mirror image points to the right. The reversal is actually in the 'depth' (front to back) dimension relative to the mirror's surface.
Get fair toss from biased coin.
If you toss twice, the probabilities of HT and TH are both (p * (1-p)). Since these are equal, assigning one to 'Heads' and the other to 'Tails' creates a fair 50/50 result.
200 fish, 99% Gold. Remove how many for 98%?
In 200 fish, 198 are gold (99%). To make them 98%, the 2 non-goldfish must represent 2% of the total. 2 is 2% of 100. So you must have 100 fish total (remove 100 gold).
Brothers Chris (FL) and Connor (OR) same time. How?
Florida has a tiny portion in Central Time, and Oregon has a portion in Mountain Time. During the DST 'fall back' hour, the times can align perfectly across the country.
How many barbershops are in the USA?
Estimate based on one barber per ~2,500 people. With a US population of 330 million, 130,000 is a standard Fermi estimation result.
How many squares on an 8x8 chessboard?
Don't just count the 1x1 squares. You must sum all possible sizes: 1x1 (64), 2x2 (49), 3x3 (36), 4x4 (25), 5x5 (16), 6x6 (9), 7x7 (4), and 8x8 (1).
How many ping pong balls fill a 747?
Estimate the volume of a 747 (approx 1000 m^3) and the volume of a ping pong ball, then account for the 'packing fraction' of empty air space between balls.
C beats T by 10m in 100m. C starts 10m back. Winner?
Since Chandler runs 100m in the same time Toni runs 90m, when Chandler is 10m back, they will meet at the 90m mark. Chandler is faster and will pull ahead in the last 10m.
Does level change when ice in water melts?
According to Archimedes, the floating ice displaces a volume of water equal to its weight. When it melts, it becomes water of that exact weight and volume.
1/2 of 2/3 of 3/4... of 9/10 of 1,000?
The series is (1/2)*(2/3)*(3/4)*...*(9/10). The numerators and denominators cancel out diagonally, leaving 1/10. 1/10 * 1,000 = 100.
Pick 1 of 3. Empty removed. Do you switch?
Your initial pick had a 1/3 chance. The remaining 2/3 chance is now concentrated in the one unopened envelope the interviewer didn't discard.
Standard deviation of {1, 2, 3, 4, 5}?
The mean is 3. Squares of deviations: (1-3)^2=4, (2-3)^2=1, (3-3)^2=0, (4-3)^2=1, (5-3)^2=4. Average is 10/5 = 2. SD is sqrt(2) ? 1.414.
HH = Jamie takes 2. Any other = Ashley takes 1. Winner?
There are 4 outcomes: HH, HT, TH, TT. HH (Jamie) happens 1/4. HT, TH, TT (Ashley) happen 3/4. Ashley wins 3 times for every 1 time Jamie wins (actually 3 coins to Jamie's 2).
Measure 4L using 3L and 5L jugs.
Fill 3, pour into 5. Fill 3 again, pour into 5 until full. 1L remains in the 3L jug. Empty 5, put that 1L in. Fill 3 and add to the 5L jug to get 4L.
Angle between clock hands at 3:15?
At 3:15, the minute hand is at 15m (90�). The hour hand has moved 1/4 of the way between 3 and 4. 30� per hour * 0.25 = 7.5�.
20% men/40% women attend. 35% employees men. Total %?
Assume 100 people: 35 men, 65 women. Attending: (20% of 35 = 7) + (40% of 65 = 26). 7 + 26 = 33 people total out of 100.
How is world population measured?
It is a combination of national censuses (counting) and statistical sampling/modeling for areas with less reliable data.
Weigh an elephant without a massive scale?
Archimedes' Principle: Put the elephant on a boat, mark the water line. Remove elephant and add stones until the boat hits the same line. Weigh the stones.
Double every 5m. 1 fills in 12h. Time for 2 to fill?
Starting with 2 is exactly where the 1-bacterium pond would be after 5 minutes (first doubling). So it saves 5 minutes off the 12-hour total.
Guess 1-1000 with higher/lower. Max guesses?
Binary search halves the search space each time. 2^10 = 1024, which covers 1-1000 in exactly 10 steps.