🔢 MathGrade 4Lesson 9
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Multiply 2- and 3-Digit Numbers

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Learning Objectives

  • 1Multiply a 2-digit number by a 1-digit number using the column method
  • 2Multiply a 3-digit number by a 1-digit number using the column method
  • 3Apply regrouping (carrying) correctly when multiplying
  • 4Estimate multiplication products to check reasonableness
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Mini Lesson

The column method (also called long multiplication) keeps digits aligned by place value so that ones, tens, and hundreds are multiplied separately and then combined. Regrouping — carrying the extra tens digit into the next column — makes this method work for any size of number.

Column Method: 2-Digit × 1-Digit

  1. Write the larger number on top, the 1-digit multiplier below the ones column, with a horizontal line underneath.
  2. Multiply the ones digit first: 7 × 6 = 42. Write 2 in the ones place; carry the 4 above the tens column.
  3. Multiply the tens digit: 4 × 6 = 24. Add the carried 4: 24 + 4 = 28. Write 28 to the left of the 2.
  4. Read the answer: 282.

Column Method: 3-Digit × 1-Digit

  1. Multiply ones first: 4 × 5 = 20. Write 0, carry 2.
  2. Multiply tens: 3 × 5 = 15. Add carried 2: 17. Write 7, carry 1.
  3. Multiply hundreds: 2 × 5 = 10. Add carried 1: 11. Write 11.
  4. Answer: 1,170.

Estimating First

  • Round the 2- or 3-digit number to the nearest ten or hundred.
  • 47 × 6: round 47 to 50 → 50 × 6 = 300. Exact answer 282 is close to 300. ✓
  • 234 × 5: round 234 to 200 → 200 × 5 = 1,000. Exact 1,170 is in the right range. ✓
  • If your exact answer is far from your estimate, check your regrouping.
Column multiplication: 47 times 6 equals 282Column Method: 47 x 6HundredsTensOnes4-47x62827x6=42: write 2, carry 4; then 4x6+4=28
47 x 6 = 282
Column multiplication: 234 times 5 equals 1,170Column Method: 234 x 5Th.H.TensOnes12-234x511704x5=20: w 0, c 2; 3x5+2=17: w 7, c 1; 2x5+1=11
234 x 5 = 1,170
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Tip: always estimate first by rounding, then use the column method. If your exact answer is far from the estimate, recheck your carries.

Vocabulary
Multiply
To find the total when groups of equal size are addede.g. Multiply 6 × 47 to find the total of six 47s.
Column method
A way to set out a multiplication so the place values line upe.g. I used the column method to multiply 234 × 5.
Regroup
To carry an extra ten into the next place valuee.g. I regrouped 42 as 4 tens and 2 ones.
Product
The answer to a multiplication probleme.g. The product of 47 and 6 is 282.
Carry
The extra digit moved to the next column when regroupinge.g. I carry the 4 above the tens column.
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