Did you know? Two is the only even prime number, while 1 is not prime at all. These facts become easy to remember when you understand what a factor means rather than memorise a long list.
Quick answer for Bukit Timah parents: Secondary 4 G1 learners should recognise prime and composite numbers, explain how factors work and make simple divisibility checks. The 2027 SEC G1 Mathematics K110 syllabus includes primes, but explicitly excludes prime factorisation.
What is a prime number?
A prime number is a positive whole number greater than 1 with exactly two distinct positive factors: 1 and itself. For example, 7 has only 1 and 7 as factors, so it is prime. A composite number has more than two factors: 8 has 1, 2, 4 and 8.
The number 1 has only one positive factor and is therefore neither prime nor composite. Zero is not prime either. Understanding the definition makes these exceptions logical.
Why 2 is the only even prime
Two has factors 1 and 2. Every larger even number also has 2 as an additional factor. For instance, 14 has 1, 2, 7 and 14. Therefore no other even number can be prime.
However, being odd does not prove a number is prime. For example, 21 is odd but divisible by 3 and 7, so it is composite. A tutor can ask a student to find one non-trivial factor to disprove a prime-number claim.
Example 1: is 29 prime?
It is not divisible by 2. Its digits sum to 11, so it is not divisible by 3. It does not end in 0 or 5, so it is not divisible by 5. Since the square root of 29 is less than 6, checking these smaller primes is enough: 29 is prime. This square-root explanation is optional mathematical insight, not a separate K110 examination requirement.
Useful divisibility checks
- By 2: the final digit is 0, 2, 4, 6 or 8.
- By 3: the sum of the digits is divisible by 3.
- By 5: the final digit is 0 or 5.
- By 10: the final digit is 0.
If 145 ends in 5, we know it is composite because 145 = 5 × 29. A number that fails the tests for 2 and 5 is not automatically prime: 49 is divisible by 7.
Example 2: rows of students
Imagine 29 students who want to stand in equal rows with at least two students in each row and at least two rows. They cannot arrange themselves in a rectangular array that meets both conditions: the only factor pair of 29 is 1 × 29. But 30 students can form 2 × 15, 3 × 10 or 5 × 6 arrangements.
This simple model makes the difference between prime and composite numbers visible. It also shows why knowing factors helps in practical packing and grouping situations.
A five-minute parent check
Try 17, 21, 27 and 31. The primes are 17 and 31; 21 = 3 × 7 and 27 = 3 × 9 are composite. Ask your child to explain each decision and solve a fresh changed-number question a day later.
What the 2027 SEC G1 syllabus really asks for
The official SEAB G1 Mathematics syllabus K110 names “negative numbers and primes” in N1 and specifically excludes prime factorisation. This guide teaches basic factor awareness to explain primality, without adding advanced factorisation methods as compulsory examination content.
SEAB’s 2027 G1 school-candidate syllabus directory lists K110 for 2027 and 4046 as the reference code for 2026 and earlier. Students sitting examinations in 2026 should use their actual registered syllabus and exam materials.
How tuition should respond to mistakes
If a student thinks 1 is prime, revisit the definition. If a student assumes all odd numbers are prime, find a small odd composite example. If they use one divisibility test and stop too soon, practise checking factors systematically. Each error needs a different correction.
The unchanged eduKateSG Clementi small-group Mathematics reference describes a three-pupil tutorial model for Secondary 1. That is a teaching reference, not confirmation of a present Secondary 4 G1 timetable or vacancy.
Frequently asked questions
Is 1 prime? No. Is 2 prime? Yes, it is the only even prime. Must G1 pupils learn prime factorisation? The 2027 syllabus excludes it.
Keep building number sense
Continue with negative numbers and roots, standard form and estimation, and the SEC K110 paper plan.