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HCF & LCM

8 questions · EasyMediumHard

The HCF is the largest number that divides all the given numbers; the LCM is the smallest number they all divide into. For two numbers, HCF × LCM equals their product.

💡 Quick tricks

  1. Find the HCF by repeated division (Euclid): HCF(84, 36) = HCF(36, 12) = 12.
  2. LCM(a, b) = a × b ÷ HCF(a, b).
  3. Bells ringing together or runners meeting at the start are LCM questions; cutting into the largest equal pieces is an HCF question.
8 questions

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Tap an answer. You'll see if it's right, and why. Easy ones come first.

  1. Q1Easy

    What is the HCF of 15 and 10?

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    Answer: B. 5

    💡 15 = 5 × 3 and 10 = 5 × 2, so the HCF is 5.

  2. Q2Easy

    What is the HCF of 35 and 20?

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    Answer: B. 5

    💡 35 = 5 × 7 and 20 = 5 × 4, so the HCF is 5.

  3. Q3Easy

    What is the HCF of 35 and 45?

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    Answer: D. 5

    💡 35 = 5 × 7 and 45 = 5 × 9, so the HCF is 5.

  4. Q4Medium

    What is the LCM of 7 and 21?

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    Answer: A. 21

    💡 HCF(7, 21) = 7, so LCM = 7 × 21 ÷ 7 = 21.

  1. Q5Medium

    What is the LCM of 23 and 9?

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    Answer: D. 207

    💡 HCF(23, 9) = 1, so LCM = 23 × 9 ÷ 1 = 207.

  2. Q6Medium

    What is the LCM of 14 and 5?

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    Answer: C. 70

    💡 HCF(14, 5) = 1, so LCM = 14 × 5 ÷ 1 = 70.

  3. Q7Hard

    What is the LCM of 15, 13 and 7?

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    Answer: C. 1,365

    💡 LCM(15, 13) = 195, and LCM(195, 7) = 1365.

  4. Q8Hard

    What is the LCM of 14, 11 and 8?

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    Answer: A. 616

    💡 LCM(14, 11) = 154, and LCM(154, 8) = 616.

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