Prime numbers

Primes have exactly two factors; composite numbers have more. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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A prime number has exactly two factors: 1 and itself. A composite number has more than two factors.

Primes up to 100 (25 primes): 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.

Watch out

1 is not prime (only one factor). 2 is the only even prime.

Careful: 91 looks prime, but 91 = 7 × 13, so it is composite.

Tap when you could tell someone without looking.

Prime factors

Break a number into primes with a factor tree: 60 = 2 × 2 × 3 × 5 = 2² × 3 × 5.

Tap when you could tell someone without looking.

Remember this: your summary

Write these points in your book. Read them again the night before the test.

Memory trick

Prime = private: only 1 and itself are invited.

Flash cards · Tap to turn over

First say the answer yourself, then turn the card over.

Now the real quiz!

The quiz has many more questions on this topic. Every question shows straight away whether you are right and explains why.

For parents

Let your child work the examples on paper and explain them to you.
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Follows CAPS for Grade 6 Mathematics. Always check your teacher’s notes and textbook too.