https://es-cl.khanacademy.org/math/cc-fourth-grade-math/imp-addition-and-subtraction-2 2025-11-20T17:53:56.044440592Z Addition, subtraction, and estimation Addition and subtraction are key skills for any math whiz. In this unit, you'll sharpen those skills by working with multi-digit numbers. You'll also learn how to round and estimate, so you can quickly make calculations even when you don't have a calculator handy. unit