Nine dots

Cards

Four-card problem
Five-card trick
Highest card
Pocket kings drawing dead
Second black ace

Geometry

Around the Earth
Belt loop
Buried powerline
Cold walks
Colored plane
Finding the river
Ghost ships
Lake monster
Planet shadow
Points and coins
Worm and the apple

Logic

10 wires
3 prisoners in a line
3 switches and a lightblub
Attacking knights
Calendar cubes
Dice groups
Flipping coins
Gold chain
Handshakes
Jewel thieves
Mislabelled marble cans
Marked prisoners
Parking lot
Party hats
Sorting hats
Spinning room
Short and tall
The bookworm

Maths

Birthday problem
Caterpillar on a bungee
Chameleons
Colliding ants
Everything equals 6
Factorial zeros
Friends at a party
Fuel circuit
Hidden ages
Hidden polynomial
Open lockers
Hiking in the mountains
Negating function

Measurement

Burning fuses
Hourglasses
Marble bags
Marble scales
Melted water bottle
Water jugs

Optimization

Airport walkway
Apple delivery
Greedy pirates
Locked pirate chest
Marble dropping

Paradox

Coin rotation
False Equations
Missing square
All horses are the same color

Physics

Disrupted scale
Find the magnet
Plane on a conveyor belt
Radioactive cookies
Resistor network
Rock in a boat

Probability

3-way shootout
Gender odds
Gender ratio
Guess the larger number
Monty hall
Prisoners' names in boxes
Prisoners with hats in a circle
Random number bluff
Red marbles, blue marbles
Seats on a plane
Tallest in line

Shapes

10x10 tiling
Broken chessboard
Cutout shapes
Cutting a square
Dividing cakes
Nine dots
Quarantine squares
Rows of trees

Simple maths

Bat and ball
Dried potatoes
Lily pads
Magic square
Squashed bee

Strategy

100 prisoners in a line
Bad processors
Bridge crossing
Catch the fugative
Table of coins
Crashing engines
Hidden salaries
Missing number
Poisoned wine bottles
Prisoners and a lightbulb
Prisoners' chessboard
River crossings
Shuffling people
Sink the sub
Spider's web

Truth

Bob and his brother
Knights and knaves
Village of knights and knaves
Shaded stones
Honest and deceitful gods

View on GitHub

Can you connect all nine dots using 4 continuous straight lines?

Nine dots

The required lines are shown in red:

Nine dots solution