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Why one is different and two is prime

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Prime Time · Distinguish primes composites and one · 3:34

You'll learn: Correct common classification mistakes

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Why one is different and two is prime

3:34

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Why one is different and two is prime

You'll learn: Correct common classification mistakes

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Same topic

Distinguish primes composites and one

1

Prime numbers have exactly two factors
3:36
Prime numbers have exactly two factors
You'll learn: Distinguish prime and composite numbers

Next topic

Identify primes systematically

2

Sift a number grid for primes
3:33
Sift a number grid for primes
You'll learn: Use a systematic sieve on a finite grid
Check a proposed prime carefully
3:30
Check a proposed prime carefully
You'll learn: Use factors and counterexamples instead of appearance

Next topic

Understand coprime numbers

3

Coprime describes a pair
3:26
Coprime describes a pair
You'll learn: Recognise two numbers sharing only factor one
Composite numbers can be coprime
3:38
Composite numbers can be coprime
You'll learn: Distinguish coprime pairs from pairs of primes
Coprime steps make a thread pattern
3:28
Coprime steps make a thread pattern
You'll learn: Explore repeated jumps around a finite peg circle

Next topic

Build and interpret prime factorisation

4

Break a number into prime building blocks
3:27
Break a number into prime building blocks
You'll learn: Continue splitting until every factor is prime
Different trees give the same prime collection
3:47
Different trees give the same prime collection
You'll learn: Check factorisation by multiplying back
Use prime tiles to check coprimality
3:42
Use prime tiles to check coprimality
You'll learn: Find shared prime factors systematically
Use prime tiles to check divisibility
3:42
Use prime tiles to check divisibility
You'll learn: Check that the divisor’s factors are all available

Next topic

Use and explain supported divisibility tests

4

Divisibility by two five and ten
3:35
Divisibility by two five and ten
You'll learn: Connect last-digit rules to place-value groups
Why the last two digits decide divisibility by four
3:38
Why the last two digits decide divisibility by four
You'll learn: Use hundreds as complete groups of four
Why the last three digits decide divisibility by eight
3:47
Why the last three digits decide divisibility by eight
You'll learn: Use thousands as complete groups of eight
Choose the right test and explain it
3:42
Choose the right test and explain it
You'll learn: Apply the supported tests without confusing their rules

Next topic

Use factors and primes in number puzzles

1

One number can be special in several ways
3:49
One number can be special in several ways
You'll learn: Justify different valid classifications