Maryland Math 3.NOS.D.6
The Standard
Estimate sums and differences within 1,000 using benchmark numbers and front-end estimation. Determine when an estimate is appropriate and when an exact answer is needed.
Maryland College and Career Ready Standards for Mathematics (2025) · USE PLACE VALUE UNDERSTANDING AND PROPERTIES OF OPERATIONS TO PERFORM MULTI-DIGIT ARITHMETIC.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students estimate three-digit sums and differences using nearby tens or hundreds, or by starting with the hundreds digits. They decide when a rough answer will do and when they need to calculate exactly.
What Mastery Looks Like
- For 438 + 357, a student starts with 400 + 300, then notices the remaining parts bring the sum close to 800. For 734 - 286, they can use 700 - 300 = 400 as a quick estimate. They know a cashier must calculate exact change.
Common Misconceptions
- Students may call 400 + 300 the exact sum of 438 + 357 because they ignore the tens and ones. Some always round both numbers down, or give an estimate when an exact count is needed.
How to Assess It
- Exit ticket: Estimate 438 + 357 using the hundreds digits and 734 - 286 using nearby hundreds. Should a cashier use either estimate to give change? Explain.
Lesson moves
Ways to Teach It
Give pairs base-ten blocks to build 438 and 357, then place 400 cards beside each model to estimate the sum.
Ask partners to write why 400 + 300 underestimates 438 + 357 and how they would adjust it.
Play Estimate Match: students pair 734 - 286 with 700 - 300 and 438 + 357 with 400 + 400, then explain each match.
Show an order for 438 pencils and 357 erasers; students estimate the total for planning, then find the exact total for the inventory sheet.
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Printable 3.NOS.D.6 Worksheet
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