The idea
Some things can't be split
LP happily says “plant 2.5 acres”. Fine for land. But you can't build 0.6 of a factory, hire 3.4 people, or accept half a project.
Integer programming (IP)An LP where some variables must be whole numbers.
Binary variableA variable that can only be 0 or 1, like a light switch. x1 = 1 means “do project 1”; x1 = 0 means “don't”.