Case studies
One output per problem. Choose a format or a domain.
All case studies (6)
MaterialEntrance-exam arithmetic (moving figures)
How far can a dog on a rope move around its kennel?
A dog is tied by a 4 m rope to the corner of a 2 m by 4 m kennel. Where the rope catches on a corner, the centre and radius of the arc change. Noticing that switch is the judgment this problem turns on. Four steps, each with a figure and the equation.
MaterialEntrance-exam arithmetic (solids of revolution)
The volume of a solid made by spinning a right triangle
A right triangle with sides 5, 12 and 13 cm is rotated once around a line. What solid appears, where is its base, and which length is its height? A one-minute animation in which the figure builds up in the order of the judgments.
MaterialU.S. case: Lucy v. Zehmer (1954)
Does “it was a joke” prevent a contract from forming?
A 1954 American case about the sale of a farm. Why did the court reject the seller’s defences that it was a joke and that he was drunk? Follow the judgments from the buyer’s claim to the ruling in a single diagram.
MaterialHarvard “Problem of the Week”
Why do two stacked balls bounce so high?
Drop a tennis ball stacked on a basketball and the tennis ball bounces to about nine times the height it fell from. Step by step, we check which conditions that answer depends on.
MaterialEntrance-exam arithmetic (solids)
The volume of a triangular pyramid from its net
Fold a 12 cm square into a triangular pyramid and find its volume. Solved in three steps, starting from spotting which edges become perpendicular when folded.
MaterialEntrance-exam arithmetic (plane figures)
Two angles in a figure made of set squares
Two set squares overlap; find the two marked angles. Solved by first writing in the fixed angles of the set squares, then using the angle sum of a triangle.