To estimate 7 × 28, round 28 to 30 and compute 7 × 30 = 210. The estimate is close to the true answer (196) and is faster to calculate mentally. Estimation checks if an answer is reasonable and supports mental math development.
You have already learned to round numbers to the nearest ten — replacing a messy number with a clean, round number nearby. Estimation in multiplication and division uses exactly that skill as its first step. The idea is to replace hard numbers with easy ones, compute quickly, and get an answer that is close enough to be useful. Estimation is not about being wrong on purpose — it is about being approximately right on purpose.
Here is the process: before multiplying or dividing, round each number to the nearest ten (or to whichever place makes the arithmetic easy). Then compute with the rounded numbers. For 7 × 28, round 28 to 30 — now you need 7 × 30, which your multiplication facts can handle instantly: 210. The real answer is 196. Your estimate is off by 14, which is less than 10% of the true answer. That is close enough to tell you your answer is in the right ballpark.
Estimation is especially powerful as a checking tool. After you do a long multiplication or division problem with pencil and paper, quickly estimate the answer. If your written answer is 1,960 but your estimate is 210, something went wrong — the two are too far apart. Estimation catches errors that you might otherwise miss. Think of it as a sanity check: "Does this answer make sense given the size of the numbers I started with?"
For division, the same logic applies: round the dividend to a nearby multiple of the divisor. To estimate 185 ÷ 6, think "what multiple of 6 is close to 185?" — 180 is 6 × 30, so the estimate is about 30. The real answer is 30.8. Estimation in division requires slightly more flexibility than in multiplication, but the core strategy is the same: find a clean version of the problem you can solve in your head.