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Brain teasers with answers.

Here are 60 brain teasers with answers: logic puzzles, number puzzles, patterns and lateral thinking problems. Every answer says how to get there, so you can explain it to the group, not just read it out.

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A girl has as many brothers as sisters. Each of her brothers has twice as many sisters as brothers. How many boys and girls are in the family?

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All 60 brain teasers with answers

Teasers tagged Run as a live quiz have one short answer and three wrong ones that look right. Talk it through teasers need explaining, so they work best out loud or in pairs.

Logic

A girl has as many brothers as sisters. Each of her brothers has twice as many sisters as brothers. How many boys and girls are in the family?
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4 girls and 3 boys The girl sees 3 sisters and 3 brothers. Each boy sees 2 brothers and 4 sisters.
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Three switches outside a closed room each control one of three lamps inside. You can go into the room only once. How do you work out which switch controls which lamp?
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Turn the first switch on for a few minutes, turn it off, turn the second one on, then go in. The lamp that’s on belongs to switch 2, the warm one that’s off to switch 1, and the cold one to switch 3.
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There are two doors: one leads out, one doesn’t. A guard stands at each. One guard always tells the truth, the other always lies, and you don’t know which is which. You can ask one guard one question. What do you ask?
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“Which door would the other guard say leads out?” Then take the other door. Both guards point you to the wrong door: the liar lies about the truth-teller, and the truth-teller reports the liar’s lie.
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A drawer holds 10 black socks and 10 white socks, all mixed up. In the dark, how many socks must you take out to be sure of a matching pair?
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3 With two colors, any three socks must include two of the same color.
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Ana finished ahead of Ben. Ben finished ahead of Dee. Cal finished behind Dee. Who came last?
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Cal The order is Ana, Ben, Dee, Cal.
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Amy says, “Ben is lying.” Ben says, “Cara is lying.” Cara says, “Amy and Ben are both lying.” Who is telling the truth?
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Only Ben If Cara were truthful, Ben would be lying, so Cara would be lying: impossible. So Cara lies, Ben is right, and Amy is wrong.
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Three boxes are labelled Apples, Oranges and Mixed. Every label is wrong. You may take one fruit from one box without looking inside. Which box do you pick from?
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The box labelled Mixed It holds only one kind of fruit. Whatever you pull out tells you what it really is, and the other two labels then fall into place.
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You have a 3-liter jug and a 5-liter jug, and plenty of water. How do you measure exactly 4 liters?
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Fill the 5, pour it into the 3, empty the 3, pour the 2 liters left into the 3, fill the 5 again and top up the 3. Topping up the 3-liter jug takes exactly 1 liter, which leaves 4 in the 5-liter jug.
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You have 9 coins that look the same, but one is slightly heavier. With a balance scale, what is the smallest number of weighings that will always find it?
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2 Weigh 3 against 3. Take the heavier group (or the 3 left over if they balance) and weigh 1 against 1.
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Ali, Bo and Cy each own one pet: a cat, a dog or a fish. Ali’s pet lives in water. Bo’s pet barks. Who owns the cat?
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Cy Ali has the fish and Bo has the dog, so the cat is Cy’s.
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On an island, knights always tell the truth and knaves always lie. You meet two islanders. The first says, “We are both knaves.” What are they?
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The first is a knave, the second is a knight A knight could never say it, so the first is a knave. His statement is a lie, so they aren’t both knaves: the second is a knight.
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Four friends must cross a narrow bridge at night with one flashlight. At most two can cross at once, and they need the light. They take 1, 2, 5 and 10 minutes, and a pair moves at the slower one’s pace. What is the shortest total time?
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17 minutes 1 and 2 cross (2), 1 returns (1), 5 and 10 cross (10), 2 returns (2), 1 and 2 cross (2).
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The day before yesterday was Thursday. What day is it today?
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Saturday Yesterday was Friday, so today is Saturday.
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In a line of people, Jo is fourth from the front and sixth from the back. How many people are in the line?
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9 3 people in front of Jo, Jo, and 5 behind: 3 + 1 + 5.
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All Bloops are Razzies, and all Razzies are Lazzies. Are all Bloops definitely Lazzies?
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Yes Every Bloop is a Razzie, and every Razzie is a Lazzie.
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Numbers

In two years, Lee will be twice as old as she was five years ago. How old is she now?
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12 12 + 2 = 14, and 12 − 5 = 7. Fourteen is twice seven.
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Five people meet, and each one shakes hands with every other person once. How many handshakes is that?
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10 4 + 3 + 2 + 1 = 10.
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A bat and a ball cost 1.10 together. The bat costs 1.00 more than the ball. How much does the ball cost?
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0.05 Ball 0.05, bat 1.05. If the ball cost 0.10, the bat would cost 1.10 and the total would be 1.20.
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If 5 machines make 5 parts in 5 minutes, how long do 100 machines take to make 100 parts?
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5 minutes Each machine makes one part in 5 minutes, however many machines there are.
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A patch of lily pads doubles in size every day. It covers the whole pond on day 48. On which day did it cover half the pond?
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Day 47 One more doubling takes it from half to all of the pond.
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A clock shows 3:15. What is the angle between the hour hand and the minute hand?
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7.5 degrees The minute hand is on the 3, but the hour hand has moved a quarter of the way to the 4: a quarter of 30 degrees.
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Which is bigger: half of a quarter, or a quarter of a half?
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They’re the same Both are one eighth.
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A train leaves at 9:00 at 60 km/h. A second train leaves the same station on the same track at 10:00 at 90 km/h. When does the second train catch up?
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12:00 At 10:00 the first train is 60 km ahead. The gap shrinks by 30 km each hour, so it closes in 2 hours.
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In a room, 7 people play chess, 5 play the piano, and 3 do both. Everyone does at least one. How many people are in the room?
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9 7 + 5 = 12, but the 3 who do both were counted twice.
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A snail climbs 3 meters up a 10-meter wall every day and slides back 2 meters every night. On which day does it reach the top?
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Day 8 After 7 nights it’s at 7 meters. On day 8 it climbs 3 meters and reaches the top before it can slide back.
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A parent is four times as old as their child. In 20 years, the parent will be twice as old as the child. How old is the child now?
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10 Child 10, parent 40. In 20 years: 30 and 60.
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A book’s pages are numbered from 1 to 100. How many times does the digit 9 appear?
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20 Ten times in the ones place (9, 19, 29 … 99) and ten times in the tens place (90 to 99).
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A clock takes 5 seconds to strike 6 o’clock. How long does it take to strike 12 o’clock?
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11 seconds Six strikes have five gaps, so each gap is one second. Twelve strikes have eleven gaps.
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You toss a fair coin five times and get heads every time. What are the chances of heads on the next toss?
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1 in 2 The coin has no memory: every toss is 50–50.
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What can you put between a 2 and a 3 to get a number bigger than 2 but smaller than 3?
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A decimal point 2.3 sits between 2 and 3.
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Patterns

What letter comes next: O, T, T, F, F, S, S, E, …?
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N They’re the first letters of one, two, three, four, five, six, seven, eight. Next is nine.
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What do the numbers 11, 69 and 88 have in common?
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They read the same upside down Turn the page over and each number still looks the same.
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What comes next: 1, 1, 2, 3, 5, 8, …?
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13 Each number is the sum of the two before it: 5 + 8.
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What comes next: 1, 4, 9, 16, 25, …?
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36 They’re square numbers: 1×1, 2×2, 3×3 and so on. Next is 6×6.
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What letter comes next: J, F, M, A, M, J, J, …?
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A The first letters of the months. After July comes August.
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Which is the odd one out: 3, 5, 7, 9, 11, 13?
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9 The others are prime numbers. 9 is 3 × 3.
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What comes next: 1, 11, 21, 1211, 111221, …?
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312211 Each line describes the one before: 111221 is “three 1s, two 2s, one 1”.
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What comes next: 3, 6, 11, 18, 27, …?
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38 The gaps grow by 2: +3, +5, +7, +9, +11.
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What comes next: AZ, BY, CX, …?
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DW The first letter moves forward through the alphabet while the second moves backward.
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What comes next: 1, 2, 6, 24, 120, …?
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720 Multiply by 2, then 3, then 4, then 5. Next is ×6.
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Which word is the odd one out: civic, level, radar, rotor, robot?
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Robot The others read the same backward.
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Which number is the odd one out: 4, 9, 16, 20, 25?
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20 The others are square numbers.
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What comes next: 1, 3, 7, 15, 31, …?
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63 Double the number and add 1.
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If A = 1, B = 2 and so on, CAT adds up to 24. What does DOG add up to?
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26 D is 4, O is 15 and G is 7.
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In a code, APPLE is written BQQMF. How is LEMON written?
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MFNPO Every letter moves one place along the alphabet.
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Lateral thinking

Someone pushes their car up to a hotel and tells the owner they’re broke. Why?
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They’re playing Monopoly The car is their playing piece, and they’ve landed on someone else’s hotel.
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A dog is on one side of a full river with no bridge and no boat. Its owner calls, and the dog crosses without getting wet. How?
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The river is frozen The river is full, but the water is frozen solid, so the dog walks across.
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Someone falls off a 6-meter ladder and doesn’t get hurt at all. How?
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They were on the bottom rung It was a step of a few centimeters.
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A rope ladder hangs over the side of a boat, with rungs 20 cm apart and three rungs underwater. The tide rises 60 cm. How many rungs are underwater now?
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Still three The boat floats, so it rises with the tide, and so does the ladder.
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Two people are born at the same moment, but they have different birthdays. How?
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They were born in different time zones When it’s just after midnight in one place, it’s still the day before somewhere else.
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Two sisters were born on the same day of the same year to the same parents, but they aren’t twins. How?
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They’re two of a set of triplets Twins means two; there was a third baby.
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A truck is stuck under a low bridge, just a few centimeters too tall. How can the driver get it free without damaging the truck or the bridge?
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Let some air out of the tires The truck sinks a little and fits under.
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Someone asks a café server for a glass of water. The server suddenly shouts “Boo!” The customer says thanks and leaves without the water. Why?
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They had hiccups The fright stopped them, so the water wasn’t needed.
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How can you drop a raw egg onto a concrete floor without cracking the floor?
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Drop it any way you like Concrete floors are very hard to crack, whatever happens to the egg.
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You throw a ball as hard as you can. It stops and comes straight back to you, though nothing touches it. How?
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You threw it straight up Gravity brings it back down.
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Someone builds a house with four walls, and every wall faces south. A bear walks past the window. What color is the bear?
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White Only at the North Pole can every wall face south, so it’s a polar bear.
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You’re driving a bus. At the first stop, 4 people get on. At the next, 2 get off and 3 get on. At the third, everyone gets off. How old is the bus driver?
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Your age The question started with “You’re driving a bus”.
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A driver with no headlights on, on a road with no streetlights and no moon, stops for someone crossing the road. How did the driver see them?
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It was daytime Nobody said it was night.
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Two people play five games of chess. Each of them wins three games. There were no draws. How?
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They weren’t playing each other Both played other opponents.
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A basket holds six eggs. Six people each take one egg, but one egg is still in the basket. How?
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The last person took the basket with the egg in it They took their egg without taking it out of the basket.
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How to run a brain teaser round with a group

Show the puzzle on screen and give people two minutes, in pairs if you can. Puzzles take longer than riddles, and talking it through is half the fun. Ask one pair to explain their answer before you show it.

In a room. Give each table a different puzzle. After three minutes, each table explains its puzzle and answer to the room, so everyone hears five puzzles for the time of one.
On a video call. Use breakout rooms of three for two minutes, then bring everyone back and ask each room for its answer before you reveal it.
In class. Number and pattern puzzles make good starters for a math lesson. Ask students to write down how they solved it, not just the answer.

Brain teasers and riddles: the difference

A riddle hides its answer in the meaning of words. A brain teaser is a puzzle you reason your way through: a logic problem, a sum with a trap in it, a pattern to complete, or a strange situation with a simple explanation.

Lateral thinking puzzles sit in between: the facts are all there, but you have to drop an assumption to see the answer. For word puzzles, see our riddles with answers.

Run brain teasers as a live quiz

In RiLiFi, a brain teaser with one answer becomes a quiz question with four options. People join from their phones with a PIN or QR code, the timer runs from 5 to 999 seconds, and faster right answers earn a speed bonus.

Give longer puzzles a longer timer. In the full-screen picker above, the four quiz options appear after you show the answer, so you can copy them into a quiz.

FAQ

Questions about brain teasers

What is a brain teaser?

A short puzzle you solve by thinking it through: a logic problem, a number puzzle, a pattern to finish, or a lateral thinking problem where you have to drop an assumption. Unlike a riddle, the answer comes from reasoning, not from a play on words.

What is a good brain teaser to start with?

“A bat and a ball cost 1.10 together. The bat costs 1.00 more than the ball. How much is the ball?” The quick answer is 0.10, but the right one is 0.05. It shows the room how a fast answer can be wrong.

Are these brain teasers good for teams at work?

Yes. Solving in pairs or small groups gets people talking, and the explanations show how different people think. None of the puzzles touch on personal topics.

How hard are these brain teasers?

They range from quick patterns that take a few seconds to logic puzzles that take a few minutes. Start with Patterns or Numbers and save Logic for when the room is warmed up.

How does the random picker work?

Press Give me a brain teaser, then press again to show the answer and how to get there, and once more for the next one. You can pick one section, such as Logic, and Full screen shows the puzzle big on a projector.

Can the group answer live?

Yes. In RiLiFi, make a quiz with the puzzle and four answers. Everyone answers from their phone, no app needed, and the leaderboard shows after each question. The free plan covers 100 players per session.