Boba Maths

Year 6 · Arithmetic skills · Skill 5B

Skill 5B: Long multiplication

Use the formal written method to multiply up to 4-digit numbers by 2-digit and 3-digit numbers.

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Each file is an editable Word document (.docx) with 25 questions in five columns. It opens in Word, Google Docs, Pages and LibreOffice, so you can change questions or add working space before printing.

Download the worksheet Download the answers Generate a new sheet for this skill

Worked examples

Long multiplication breaks a multiplication into easier ones: multiply by the ones, then the tens, then the hundreds, and add the rows. A zero placeholder keeps every digit in the correct column.

Example 1

3-digit × 2-digit

346 × 27

  1. Estimate first: 346 is close to 350 and 27 is close to 30. 350 × 30 = 10,500.
  2. Multiply by each digit of the bottom number, starting with the ones. For the tens digit, write a 0 in the ones place first (a placeholder), because we are really multiplying by a multiple of 10. For the hundreds digit, write two zeros.
       346
      × 27
    ------
      2422   ← 346 × 7
      6920   ← 346 × 20
    ------
      9342
  3. Each row is a partial product: 346 × 7 = 2,422; 346 × 20 = 6,920.
  4. Add the rows: 2,422 + 6,920 = 9,342.
  5. The answer is 9,342, which is close to the estimate of 10,500.

Answer: 9,342

Example 2

4-digit × 3-digit

2,138 × 146

  1. Estimate first: 2,138 is close to 2,000 and 146 is close to 150. 2,000 × 150 = 300,000.
  2. Multiply by each digit of the bottom number, starting with the ones. For the tens digit, write a 0 in the ones place first (a placeholder), because we are really multiplying by a multiple of 10. For the hundreds digit, write two zeros.
        2138
       × 146
    --------
       12828   ← 2138 × 6
       85520   ← 2138 × 40
      213800   ← 2138 × 100
    --------
      312148
  3. Each row is a partial product: 2,138 × 6 = 12,828; 2,138 × 40 = 85,520; 2,138 × 100 = 213,800.
  4. Add the rows: 12,828 + 85,520 + 213,800 = 312,148.
  5. The answer is 312,148, which is close to the estimate of 300,000.

Answer: 312,148

Top tips

  • Put in the placeholder zero before you multiply the tens row.
  • Keep columns tidy; squared paper helps.
  • An estimate will tell you if you are way out.

Watch out for

  • Forgetting the placeholder zero, so the tens row is ten times too small.
  • Adding the rows without checking the columns line up.

Try some questions

These are from the worksheet. Work each one out, then open it to check.

  1. 124 × 12 =
    Show the answer

    1,488

  2. 268 × 21 =
    Show the answer

    5,628

  3. 1,345 × 124 =
    Show the answer

    166,780

  4. 2,789 × 245 =
    Show the answer

    683,305

All arithmetic skills

Arithmetic skills overview · Year 6 overview