Q1
Which of these is a prime number?
A7
B8
C9
D10
CBSEClass 6 (CBSE)MathematicsCh 5 · Topic 1
Prime and Composite Numbers
Learning to identify prime and composite numbers.
Core concept
Interestingly, 2 is the only even prime number — every other even number greater than 2 is composite, since it is always divisible by 2 in addition to 1 and itself. The ancient method called the 'Sieve of Eratosthenes' systematically eliminates composite numbers from a list, leaving only primes — this method involves crossing out multiples of each prime starting from 2, revealing the primes up to a chosen limit.
Exam highlight
Key diagram
- Show a sieve-of-Eratosthenes style grid highlighting prime numbers up to 50.
Keywords worth remembering
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Study resources
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Quick notes
• Prime numbers have exactly 2 factors: 1 and itself (e.g., 2, 3, 5, 7).
• Composite numbers have more than 2 factors (e.g., 4, 6, 8, 9).
• 1 is neither prime nor composite.
• 2 is the only even prime number; all other even numbers are composite.