Maryland Math 2.NOS.A.5
The Standard
Estimate quantities by reasoning about their location on a number line, their relationship to benchmark numbers (e.g. 10, 50, 100), and to assess reasonableness of sums and differences.
Maryland College and Career Ready Standards for Mathematics (2025) · UNDERSTAND PLACE VALUE AND REPRESENTATIONS OF NUMBERS.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students place numbers on a number line using 10, 50, and 100 as anchors. They use nearby numbers to estimate sums and differences and check whether answers make sense.
What Mastery Looks Like
- A student places 47 just before 50 and explains why 47 + 32 should be close to 80. They can tell that 19 is not a reasonable answer.
Common Misconceptions
- Some students space 10, 50, and 100 evenly on a number line. Others treat an estimate as an exact answer or check only the digits in an answer, not its size.
How to Assess It
- On a line labeled 0, 50, and 100, place 47 and 32. Is 47 + 32 = 19 reasonable? Explain using a nearby number.
Lesson moves
Ways to Teach It
Tape a floor line labeled 0, 50, and 100; pairs place 47 and 32 cards, then mark their estimated sum.
Ask, “Could 83 minus 39 equal 12?” Have students write one sentence using nearby tens to explain their answer.
Show 58 + 21 and cards labeled 50, 80, and 120; teams point to the best estimate and explain their choice.
Give students two pencil order slips, for 47 and 32 pencils; ask whether an 80-pencil carton can hold both orders.
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Printable 2.NOS.A.5 Worksheet
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Related Standards
- 4.NOS.A.1.b
Estimate quantities by reasoning about their location on a number line, their relationship to benchmark numbers, and rounding to any place.
- 6.NOS.C.6.a
Estimate quantities by reasoning about their location on a number line, their relationship to benchmark numbers, and by rounding.
- 5.NOS.A.3.b
Estimate decimal quantities by reasoning about their location on a number line, their relationship to benchmark numbers (e.g. 0, 0.25, 0.5, 0.75, 1) and roundin...
- 3.NOS.A.1.c
Estimate quantities by reasoning about their location on a number line, their relationship to benchmark numbers, and rounding to nearest 10 or 100.
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