Understanding that prime numbers have exactly two factors (1 and itself), identifying primes up to 100.
Where your child meets this in real life: Understanding factors, cryptography basics, and number theory puzzles
SEAGReady breaks prime numbers into 2 steps, taught in order so each skill builds on the last.
Understand that prime numbers have exactly two factors (1 and itself), and identify all primes from 2 to 20
Test whether larger two-digit numbers are prime by systematic divisibility checking
Three free sample questions from our prime numbers course. Every question comes with a full explanation, and hints that guide without giving the answer away.
Sean is learning about prime numbers. His teacher asks him to check whether 7 is prime by listing its factors. What are the factors of 7?
Answer: A. 1 and 7 only
To find factors of 7, check which numbers divide into 7 exactly: 7 divided by 1 = 7 (yes, 1 is a factor) 7 divided by 2 = 3.5 (no) 7 divided by 3 = 2.33... (no) 7 divided by 7 = 1 (yes, 7 is a factor) The only factors of 7 are 1 and 7. Since 7 has exactly two factors, it is a prime number.
Stuck? Start here: A factor divides into the number with no remainder. Try dividing 7 by different numbers.
Rory wants to check if 51 is prime. He tests if it divides by small primes. The digit sum of 51 is 5 + 1 = 6. Since 6 is divisible by 3, what can Rory conclude?
Answer: A. 51 is divisible by 3, so 51 is not prime
Using the digit sum rule: Add the digits: 5 + 1 = 6 6 is divisible by 3 (6 divided by 3 = 2) So 51 must also be divisible by 3. Let's check: 51 divided by 3 = 17 This means 51 = 3 times 17 So 51 has factors: 1, 3, 17, 51 (four factors) 51 is NOT prime.
Stuck? Start here: The digit sum rule: if the digits add up to a multiple of 3, the number divides by 3.
Aoife needs to decide if 13 is a prime number. She lists its factors as 1 and 13. Is 13 prime?
Answer: A. Yes, because it has exactly two factors
A prime number has exactly two factors: 1 and itself. Aoife correctly found that 13 has factors: 1 and 13. That's exactly two factors. So 13 IS a prime number. The reason isn't that it's odd or big - it's because it has exactly two factors.
Stuck? Start here: Remember the definition: a prime number has exactly how many factors?
This is the exact interactive worked example your child sees in SEAGReady. Step through it and watch the method build up.
Ciara is learning about special numbers. Her teacher asks her to decide whether 11 is a prime number.
Is 11 a prime number? Explain by listing its factors.
11 = ? x ?
Step 1 of 4
Ciara is learning about special numbers. Her teacher asks her to decide whether 11 is a prime number.
Is 11 a prime number? Explain by listing its factors.
11 is a prime number because it has exactly two factors: 1 and 11.
The key insight: Prime means exactly TWO factors - that's why 1 is not prime (only one factor)!
Watch out: 1 is a prime number. 1 only has one factor (itself), but primes need exactly two different factors.
These are the misconceptions we see most often in prime numbers, including the ones our practice questions are specifically designed to catch.
Struggling with prime numbers? The real gap is often in one of these earlier topics.
SEAGReady finds the exact step where your child gets stuck, teaches it with worked examples like the one above, and brings it back for review so it sticks.