Estimation Fundamentals

Mental Math · Axiom Academy

LESSON Estimation Fundamentals When you don't need the exact answer — round to friendly numbers, compute fast, and know which way your estimate leans. Suppose you want 487 plus 312 . Round each number to the nearest hundred — 487 becomes 500, and 312 becomes 300 — then add the friendly numbers. Because 500 and 300 are round, the sum is instant. round each to the nearest hundred, then add A good estimate comes with a direction . Rounding a number up makes it bigger than the real value, so it pushes your answer over . Rounding down makes it smaller, so it pushes your answer under . The final lean is the tug-of-war between those pushes. The friendly number is a little too big, so the estimate ends up a little too big. The friendly number is a little too small, so the estimate ends up a little too small. 3. Front-End: The Fastest, Lowest Estimate When you want a number even faster, keep only the first digit of each and treat the rest as zeros. For 627 plus 891 , that is just 600 plus 800. It is the quickest estimate of all — and it comes with a guarantee. Front-end only ever throws digits away — it never adds anything back. So the estimate can't overshoot: it is a floor the true answer always sits on top of. That makes it perfect for a quick "is it at least this much?" check. 4. Compatible Numbers for Multiplying

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