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Study with Ghada› Math Fifth Grade, Primary› Unit 2

Lesson ⁦2-2⁩: Estimate Sums and Differences

Math · Fifth Grade, Primary · Unit 2: Addition and Subtraction · First Semester

A 10-question quiz; after every question you'll see the right answer with an explanation.
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What will you learn in this lesson?

Students use rounding to quickly estimate sums and differences of whole numbers and decimals. Estimating helps judge whether an answer is reasonable before calculating exactly.

  • Estimates sums and differences of whole numbers by rounding
  • Estimates sums and differences of decimals
  • Uses estimation to check whether an answer is reasonable

💡 Tip: Round each number first, then add or subtract the rounded numbers. Rounding the result after an exact calculation is not estimating.

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Worked examples from the Estimate Sums and Differences lesson questions

Estimate 487 + 312 by rounding to the nearest hundred.
  • 800
  • 700
  • 900
  • 799
✓ 800
487 ≈ 500 and 312 ≈ 300, so 500 + 300 = 800.
Estimate 8,725 − 3,190 by rounding to the nearest thousand.
  • 6,000
  • 5,000
  • 12,000
  • 5,500
✓ 6,000
8,725 ≈ 9,000 and 3,190 ≈ 3,000, so 9,000 − 3,000 = 6,000.
Show more examples (3)
Estimate 6.8 + 2.3 by rounding to the nearest whole number.
  • 9
  • 8
  • 10
  • 9.1
✓ 9
6.8 ≈ 7 and 2.3 ≈ 2, so 7 + 2 = 9.
Estimate 15.72 − 4.39 by rounding to the nearest whole number.
  • 12
  • 11
  • 20
  • 11.33
✓ 12
15.72 ≈ 16 and 4.39 ≈ 4, so 16 − 4 = 12.
Hind bought a dress for 189 riyals and shoes for 112 riyals. Estimate what she paid by rounding to the nearest hundred.
  • 300 riyals
  • 200 riyals
  • 400 riyals
  • 301 riyals
✓ 300 riyals
189 ≈ 200 and 112 ≈ 100, so 200 + 100 = about 300 riyals.

FAQ about the Estimate Sums and Differences lesson

How do I estimate 487 + 312?

Round each number to the nearest hundred: 500 + 300 = 800, so the actual sum is close to 800.

What's the point of estimating if I can calculate exactly?

Estimating catches mistakes. If you calculate 6.8 + 2.3 and get 30.1, the estimate 7 + 2 = 9 tells you your answer isn't reasonable.

How do I study the lesson Estimate Sums and Differences and test myself on it?

Start the lesson quiz on Study with Ghada: 10 questions from the Math Fifth Grade, Primary question bank. After each answer you'll see the right answer with an explanation, and any questions you miss move to “Review my mistakes” until you master them.

Are Study with Ghada quizzes free and aligned with the curriculum?

Yes, completely free. They're built on the Math - Grade 5 - Semester 1 lessons in the same order as the book, and every question is reviewed and approved by a teacher before students see it.

Unit 2 lessons: Addition and Subtraction

⁦2-1⁩ Round Numbers and Decimals ⁦2-3⁩ Problem-Solving Strategy: Work Backward ⁦2-4⁩ Add and Subtract Decimals ⁦2-5⁩ Addition Properties ⁦2-6⁩ Mental Addition and Subtraction All Math Fifth Grade, Primary lessons →
← ⁦2-1⁩ Round Numbers and Decimals ⁦2-3⁩ Problem-Solving Strategy: Work Backward →