https://www.khanacademy.org/math/cc-fourth-grade-math-essentials/xcc712acd200f2b6c:addition-subtraction-and-estimation 2026-06-30T17:10:42.766349973Z 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