A mathematical puzzle centered around the manipulation and solution of equations.
Algebra is the study of mathematical symbols and the rules for manipulating these symbols. Puzzles where equations, variables, polynomials, vectors, or matrices, feature prominently should typically include this tag.
Example: Some birds are sitting in two trees. The birds in the first tree say to the others: "If one of you comes to our tree, our number will be twice your number." The birds in the second tree say: "If one of you comes here, our number will be equal to yours." How many birds are in each tree?