Estimation Strategy Examples

Mental Math · Axiom Academy

EXAMPLE Estimating 487 + 312 by Rounding Round each addend to the nearest hundred for a fast estimate — then check your understanding of two more quick strategies: front-end estimation and compatible numbers. Estimate 487 + 312 using rounding: round each addend to the nearest hundred, then add the rounded values to get a fast, reasonable estimate. Excellent work — you've learned three powerful estimation strategies. Here's when to reach for each one: Rounding is best for addition and subtraction — round each number to a convenient place value (tens, hundreds, thousands), then combine the rounded values. Front-end estimation is ideal for large numbers — keep only the leading digit of each number and zero out the rest for a fast first estimate, then refine it if you want more accuracy. It tends to underestimate. Compatible numbers shine for multiplication and division — swap in a nearby number that's easy to work with mentally (like 50 instead of 48 , since 50 is half of 100 ). The goal is a reasonable answer fast, not an exact one — a good estimate lets you sanity-check a calculation or make a quick decision. Today's results: (exact: 799 ) by rounding; (exact: 6 , 259 ) by front-end estimation; (exact: 336 ) by compatible numbers. Every strategy trades a little precision for a lot of speed — with practice, you'll instinctively reach for whichever one fits the numbers in front of you.

This is the written version of the interactive lesson above. See the full Mental Math course.