Estimation

Grade 3 · mathematics · 70 practice problems · read aloud

🔊 Listen to this explanation

What is Estimation? 🤔

Estimation is making a smart guess that is close to the exact answer. We use it when we don't need a perfect number, just one that is about right. It's super useful for checking if your final answer makes sense, or for quick calculations in your head!

How to Estimate: A Step-by-Step Guide

  1. Look at the numbers. Find the digit in the tens place.
  2. Apply the Rule of Rounding.
    • If the digit in the ones place is 0, 1, 2, 3, or 4, round down to the nearest ten.
    • If the digit in the ones place is 5, 6, 7, 8, or 9, round up to the nearest ten.
  3. Do the math with your new, rounded numbers.

Let's Try Some Examples!

Example 1: 47 + 32

Step 1: 47 rounds up to 50. (Because of the 7 in the ones place).

Step 2: 32 rounds down to 30. (Because of the 2 in the ones place).

Step 3: 50 + 30 = 80. Our estimate is 80! (The real answer is 79, so we're very close!).

Example 2: 83 - 28

Step 1: 83 rounds down to 80.

Step 2: 28 rounds up to 30.

Step 3: 80 - 30 = 50. Our estimate is 50! (The real answer is 55).

⚠️ Common Mistakes to Avoid

  • Forgetting to round first: Always round numbers before you add or subtract.
  • Rounding incorrectly: Remember the rule! 0-4 round down, 5-9 round up. A number like 35 rounds up to 40.
  • Confusing exact and estimate: Your estimate is a helpful guess, not the final answer.

🌟 Tips & Tricks

  • 5 or more, let it soar! 4 or less, let it rest! This rhyme helps you remember when to round up or down.
  • Use estimation as a "number sense" check. If your exact answer is 12 but your estimate was 60, you know something went wrong!
  • Practice with prices at the store. If a toy costs $19, it's about $20.

How to Practice

Become an Estimation Expert!

  • Ask a grown-up to give you two 2-digit numbers to add or subtract. Round them first!
  • Look for numbers in your daily life—on signs, in books, on the clock—and practice rounding them in your head.
  • Play online estimation games that make practicing fun.

Practice problems

6 of the 70, worked through step by step — try them before opening the answer.

1 324 + 587 = ?

Hint: When adding larger numbers, start with the ones place and remember to carry over if needed.

Show the answer

Answer: 911

  1. Write the numbers one under the other, aligning the digits by place value (ones, tens, hundreds). 324 + 587
  2. Add the ones column (rightmost column): 4 + 7 = 11. Write down the 1 in the ones place of the answer, and carry over the 1 (which is 10) to the tens column. Ones: 4 + 7 = 11 → write 1, carry 1 to tens.
  3. Add the tens column: 2 + 8 = 10, plus the carried 1 makes 11. Write down the 1 in the tens place of the answer, and carry over the 1 (which is 100) to the hundreds column. Tens: 2 + 8 = 10, plus carried 1 = 11 → write 1, carry 1 to hundreds.
  4. Add the hundreds column: 3 + 5 = 8, plus the carried 1 makes 9. Write down the 9 in the hundreds place. Hundreds: 3 + 5 = 8, plus carried 1 = 9 → write 9.
  5. Combine the digits from each column: hundreds digit is 9, tens digit is 1, ones digit is 1. So the result is 911. Final answer: 911

Let's add 324 and 587 step-by-step.

2 245 + 387 = ?

Hint: When adding larger numbers, start with the ones place and remember to carry over if the sum is 10 or more.

Show the answer

Answer: 632

  1. Write the numbers one above the other, aligning the digits by place value (ones, tens, hundreds). 245 387 ---
  2. Add the ones column (rightmost column). 5 + 7 = 12 12 is 10 + 2. Write down the 2 in the ones place of the answer, and carry over the 1 (which is 1 ten) to the tens column. Answer so far: ___2 Carry: 1
  3. Add the tens column (middle column). We have: 4 + 8 + the carried 1 = 13 13 is 10 + 3. Write down the 3 in the tens place of the answer, and carry over the 1 (which is 1 hundred) to the hundreds column. Answer so far: __32 Carry: 1
  4. Add the hundreds column (leftmost column). We have: 2 + 3 + the carried 1 = 6 Write down the 6 in the hundreds place. Answer so far: 632
  5. Final check. 245 + 387 = 632. Therefore,

Let's add 245 and 387 step-by-step. the correct answer is 632.

3 Estimate: 673 - 298 (round to nearest 100)

Hint: Round each number to the nearest hundred first, then subtract the rounded numbers.

Show the answer

Answer: 400

  1. Round 673 to the nearest hundred. 673 is closer to 700 than to 600, so it rounds to 700.
  2. Round 298 to the nearest hundred. 298 is closer to 300 than to 200, so it rounds to 300.
  3. Subtract the rounded numbers: 700 - 300 = 400. The estimated difference is 400.

4 Estimate: 357 + 489 (round to nearest 100)

Hint: Think about rounding each number to the nearest hundred first. Look at the tens digit to decide whether to round up or down.

Show the answer

Answer: 900

  1. Round 357 to the nearest 100. The tens digit is 5, so we round up. 357 rounds to 400.
  2. Round 489 to the nearest 100. The tens digit is 8, so we round up. 489 rounds to 500.
  3. Add the rounded numbers: 400 + 500 = 900. The estimated sum is 900.

5 Estimate: 462 + 538 (round to nearest 100)

Hint: Think about rounding each number to the nearest hundred first, then add the rounded numbers.

Show the answer

Answer: 1000

  1. Round 462 to the nearest 100. 462 is between 400 and 500. Since the tens digit is 6 (which is 5 or more), round up to 500.
  2. Round 538 to the nearest 100. 538 is between 500 and 600. Since the tens digit is 3 (which is less than 5), round down to 500.
  3. Add the rounded numbers: 500 + 500 = 1000. The estimated sum is 1000.

6 Estimate: 589 - 312 (round to nearest 100)

Hint: Round each number to the nearest hundred first, then subtract the rounded numbers.

Show the answer

Answer: 300

  1. Round 589 to the nearest 100. The tens digit is 8, which is 5 or more, so round up to 600.
  2. Round 312 to the nearest 100. The tens digit is 1, which is less than 5, so round down to 300.
  3. Subtract the rounded numbers: 600 - 300 = 300. The estimated difference is 300.
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