Mental calculation strategies · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Mental maths: breaking big problems apart

Mathematics · Multiplication & Division · ages 10-11
Name ______________________   Date ____________

  1. Work out 45 x 8 mentally.

    Answer: ______________

  2. Which of these equals 45 x 8?

    • 40 x 5 + 8
    • 40 x 8 + 5 x 8
    • 45 + 45 + 8
    • 40 x 8 + 5

  3. What is 45 split into for an easy multiplication by 8?

    • 44 and 1
    • 40 and 5
    • 50 and -5

  4. In 250×3+500, you should add 500 to 250 before multiplying by 3.

    Circle one:   True   False

  5. Work out 38 x 6 mentally.

    Answer: ______________

  6. Work out 250×3+500 by choosing the correct order of steps.

    • Add 250+500 first, then multiply by 3
    • Multiply 250×3 first, then add 500
    • Add 3+500 first, then multiply by 250

  7. Noah says 6.5 x 4 = 26 because 65 x 4 = 260 and the answer is ten times smaller. Is Noah right?

    Circle one:   True   False

  8. Ava says 38 x 6 = 240 - 12 because 38 is 2 less than 40. Is Ava right?

    Circle one:   True   False

  9. Maya splits 45×8 into 40×8=320 and 5×8=40, but writes her final answer as 320. What mistake did she make?

    • She multiplied 5×8 wrong
    • She split 45 the wrong way
    • She forgot to add the two parts together

  10. Which way finds 99 x 7 fastest?

    • 100 x 7 - 7
    • 99 x 7 + 7
    • 90 x 7 + 9
    • 99 + 99 + 7
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Mental maths: breaking big problems apart W1-mt_vmW2cb5c7A-s1

  1. 360 · 40 x 8 = 320 and 5 x 8 = 40, giving 360.
  2. 40 x 8 + 5 x 8 · Splitting 45 into 40 and 5 gives 40 x 8 + 5 x 8 = 320 + 40 = 360.
  3. 40 and 5 · 40 and 5 both work well with 8, since 40×8 and 5×8 are quick facts. 40 + 5 still equals 45.
  4. False · Multiplication comes first here: 250×3=750, then you add 500 to get 1250.
  5. 228 · 40 x 6 = 240, minus 2 x 6 = 12, giving 228.
  6. Multiply 250×3 first, then add 500 · Multiplication happens before addition here: 250×3=750, then 750+500=1250.
  7. True · Noah is right: 6.5 is 65 divided by 10, so the product is 260 divided by 10.
  8. True · Ava is right: 40 x 6 = 240 overshoots by 2 sixes, so subtract 12 to get 228.
  9. She forgot to add the two parts together · Both parts need adding at the end: 320+40=360. Maya stopped one step too early.
  10. 100 x 7 - 7 · Round 99 to 100: 100 x 7 = 700, minus one 7 gives 693.
Worksheet · LightMySky