Where this idea comes from
Pheasants and rabbits
A Chinese book of arithmetic, The Mathematical Classic of Master Sun (Sunzi Suanjing), written between about the 3rd and 5th centuries, asks: pheasants and rabbits share a cage, with 35 heads and 94 feet below — how many of each?
One thing to hold: A cage, heads on top, feet underneath.
Why it matters: One trick: ask every animal to lift two feet. The pheasants are now standing on nothing, so every foot still down belongs to a rabbit, two each. Guess and check gets there too — the trick shows why the numbers move the way they do.
What we don’t know: Nobody knows who Master Sun was or exactly when the book was written.