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Grade 10 Math — Real numbers

Use Euclid's division lemma and prime factorisation to find HCF and LCM, and tell a rational number from an irrational one.

Name: ________________________

Before you start

Move along this line between 1 and 2, a tenth at a time. Every tick you land on is a fraction — a whole number over a whole number.

1.01.11.21.31.41.51.61.71.81.92.0

√2 is about 1.414, so it hides between two of these ticks. Make the steps ten times finer and it hides between two of those instead. It never lands on one, and that is exactly what irrational means.

  1. 1.Match each number to its prime factorisation.

    • 36
    • 60
    • 84
    • 90
    • 2² × 3 × 5
    • 2 × 3² × 5
    • 2² × 3²
    • 2² × 3 × 7

  2. 2.Euclid's division lemma says that for whole numbers a and b there are whole numbers q and r with a = bq + r, where r is smaller than b. Divide 455 by 42. What is the remainder?

  3. 3.√2 is neither a whole number nor a fraction, so it sits between two ticks on this line. Tap the tick just below it.

    Mark the line with an X.

    1.01.11.21.31.41.51.61.71.81.92.0

  4. 4.Find the HCF of 616 and 32 using Euclid's algorithm.

  5. 5.Find the HCF of 6, 72 and 120.

  6. 6.Find the LCM of 12 and 18.

  7. 7.For any two numbers, HCF × LCM equals the product of the numbers. The HCF of two numbers is 9 and their LCM is 360. One of the numbers is 45. What is the other?

  8. 8.13/125 has a decimal expansion that stops. After how many decimal places does it stop?

    • a) 2
    • b) 1
    • c) 4
    • d) 3

Answer key — Grade 10 Math — Real numbers

  1. 1. 36 → 2² × 3²; 60 → 2² × 3 × 5; 84 → 2² × 3 × 7; 90 → 2 × 3² × 5
  2. 2. 35
  3. 3. 1.4
  4. 4. 8
  5. 5. 6
  6. 6. 36
  7. 7. 72
  8. 8. d) 3