Maryland Math 4.NOS.E.12.b
The Standard
- 4.NOS.E.12
- Apply and extend previous understanding of addition and subtraction of whole numbers to add and subtract fractions with like denominators.
Estimate sums and differences by reasoning about benchmark numbers and assess reasonableness of answers (e.g., 3/4 + 3/4 will be greater than 1 because both fractions are greater than 1/2).
Maryland College and Career Ready Standards for Mathematics (2025) · BUILD FRACTIONS FROM UNIT FRACTIONS BY APPLYING AND EXTENDING PREVIOUS UNDERSTANDINGS OF OPERATIONS ON WHOLE NUMBERS.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students use 0, 1/2, and 1 to estimate fraction sums and differences without finding exact answers. They use those estimates to check whether an answer makes sense.
What Mastery Looks Like
- A student can tell that 3/4 + 2/3 is greater than 1 because both fractions exceed 1/2. They estimate 7/8 - 2/5 at about 1/2 and reject an answer near 0.
Common Misconceptions
- Some students add denominators and write 3/4 + 3/4 = 6/8, missing that the sum exceeds 1. Others round 2/5 down to 0 when estimating, which makes a difference too large.
How to Assess It
- Ask: “Estimate 7/8 - 2/5 using benchmarks. Could the answer be 1/8? Explain.”
Lesson moves
Ways to Teach It
Give pairs paper fraction strips for 3/4 and 2/3; have them line up the strips against a whole strip to estimate the sum.
Ask, “Could 7/8 - 2/5 be 1/8? Explain using 1/2 as a benchmark.”
Give pairs cards labeled 3/4 + 2/3, 7/8 - 2/5, and 1/4 + 1/8; race to rank their estimates from least to greatest.
Show a recipe with 3/4 cup oats and 2/3 cup flour; ask whether their total is more or less than 1 cup.
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Printable 4.NOS.E.12.b Worksheet
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