The primary sector involves activities that:

produce goods directly from nature

Which of these belongs to the secondary sector?

Manufacturing cloth from cotton in a factory

What is a prime number?

A number that has exactly two factors, namely 1 and the number itself, such as \(2, 3, 5, 7, 11\).

What is a composite number?

A number with more than two factors, such as \(4, 6, 8, 9\); it has at least one factor other than 1 and itself.

Is 1 a prime or a composite number?

Neither; 1 has only one factor and is neither prime nor composite.

What is the only even prime number?

2 is the only even prime number; every other even number has 2 as an extra factor.

What is the Sieve of Eratosthenes?

A method of finding primes by crossing out multiples of each prime in turn, leaving the prime numbers circled.

How can prime factorisation tell if two numbers are co-prime?

If their prime factorisations share no common prime factor, the numbers are co-prime; otherwise they are not.

Numbers divisible by 5 end in which digits?

Numbers divisible by 5 end with either 0 or 5.

How do you test if a number is divisible by 4?

Check whether the number formed by its last two digits is divisible by 4; if so, the whole number is divisible by 4.

CBSE Class 6 Annual Assessment

Q: What does it mean for two numbers to be co-prime?

They are co-prime if their only common factor is 1, for example 4 and 9.

Annual assessment for Class 6 students under CBSE, covering core subjects like Mathematics, Science, Social Science, English, and Hindi, focusing on foundational knowledge and skills.

Prime Time — Class 6 Mathematics

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Mathematics · 10 chapters

Summary, key terms, important questions and a practice quiz with AI diagnosis for each.

CBSE Class 6Mathematics Ganita Prakash

Chapter 5: Prime Time

Summary

This chapter develops factors, multiples and prime numbers through games. The idli-vada game introduces common multiples of two numbers, and treasure-hunting jumps introduce common factors and divisors. A prime number has exactly two factors \u2014 1 and itself \u2014 so the first primes are \(2, 3, 5, 7, 11, 13, \dots\); numbers with more than two factors are composite, and 1 is neither prime nor composite. The Sieve of Eratosthenes is used to list all primes up to 100. Two numbers are co-prime if their only common factor is 1, for example 4 and 9. The chapter introduces prime factorisation: every number greater than 1 can be written as a product of primes in only one way apart from order, e.g. \(56 = 2 \times 2 \times 2 \times 7\). Prime factorisation is then used to test whether two numbers are co-prime and whether one number divides another. Finally, simple divisibility tests for 10, 5, 2, 4 and 8 are derived by looking at the last one, two or three digits. The chapter also explores perfect numbers, twin primes and prime puzzles.

Common Multiples and Common FactorsPrime and Composite NumbersSieve of EratosthenesCo-prime NumbersPrime FactorisationDivisibility Tests

Key terms

Factor

A number that divides another number exactly, leaving no remainder; e.g. 4 is a factor of 12.

Multiple

The product of a number with a counting number; e.g. 12, 24, 36 are multiples of 12.

Prime number

A number with exactly two factors, 1 and itself, such as \(2, 3, 5, 7, 11\).

Composite number

A number with more than two factors, such as \(4, 6, 8, 9, 10\).

Co-prime numbers

Two numbers whose only common factor is 1, such as 4 and 9.

Prime factorisation

Writing a number as a product of prime numbers, e.g. \(84 = 2 \times 2 \times 3 \times 7\).

Important questions

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Factor

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Meaning1 / 6

A number that divides another number exactly, leaving no remainder; e.g. 4 is a factor of 12.

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Practice quiz · Prime Time

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Prime Time

Maths 10 Qs · ~10 min