crane-tortoise calculation; solving for two unknowns from totals
A classic Japanese math problem: given the total number of heads and legs of cranes and tortoises, find how many of each. By extension, any problem of solving for two unknowns from their total count and the total of one attribute.
The crane-tortoise calculation is a problem often used in Edo-period Japanese mathematics.
This problem can be solved using the crane-tortoise calculation.