Primes, HCF and LCM practice questions

Secondary 1 topics, the foundation the O-Level Mathematics 4052 syllabus builds on. Every question below has a full worked solution.

When a student gets a question wrong in Math Amigo, it does not show the answer straight away. It reads the working, identifies the step that went wrong, and asks a question that points at the correction. The worked solution is there once a genuine attempt has been made.

Practise primes, hcf and lcm free

What this topic covers

Worked examples

Example 1

Is 7777 a prime number or a composite number?
Show the worked solution
  • We test divisibility by primes up to $\sqrt{77} = 8.77\quad \scriptsize\text{(to 2 d.p.)}\quad \scriptsize\textit{trial division}$
  • $77 \div 7 = 11 \quad \scriptsize\textit{exact division found}$
  • $77 = 7 \times 11$
  • Therefore, $77$ is <b>composite</b>. Its smallest prime factor is $7$.

Answer: compositecomposite

Example 2

Express 175175 as a product of its prime factors in index notation.
Show the worked solution
  • $175 \div 5 = 35 \quad \scriptsize\textit{repeated division}$
  • $35 \div 5 = 7$
  • $7 \div 7 = 1$
  • $175 = 5 \times 5 \times 7$
  • $= 5^{2} \times 7 \quad \scriptsize\textit{index notation}$

Answer: 52×75^2 × 7

Example 3

455455 unit cubes are arranged to form a cuboid. Given that 455455 can be expressed as a product of 3 prime numbers, find the dimensions of the cuboid.
Show the worked solution
  • $455 = 5 \times 7 \times 13 \quad \scriptsize\textit{prime factorisation}$
  • The three prime factors are $5$, $7$, and $13$.
  • Dimensions of the cuboid: $5 \times 7 \times 13$

Answer: 5,7,135,7,13

Questions parents ask

Is it really free?

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Which syllabus does this follow?

O-Level Mathematics (4052), for Singapore secondary students. Math Amigo covers Secondary 1 to 4, both O-Level Mathematics and Additional Mathematics.

Will it just show my child the answer?

No. On a wrong answer it looks at the working, points to the step that went wrong, and asks a question that helps the student find the correction. The full worked solution is available after a genuine attempt.

Other Secondary 1 topics