Divisors prime factorisation prime numbers
Age Group
15 16
Expected time
1 period
Your numbers divided.PDF
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Your numbers divided

What’s the mystery? You are able to predict numbers that exactly divide a series of random numbers chosen by students.
Domain(s) Mathematics
Subdomain keywords Divisors, prime numbers, prime factorisation.
Age group 15 to 16 years old.
Expected time for the mystery Approximate time for teacher preparation: ten min.Approximate time in classroom: one hour.
Safety/supervision NoneDisclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials Calculators or student mobile phones if allowed in class.
Learning objectives Students will understand prime numbers and prime factors of numbers.
Resources Videos showing this trick, among others, being performed and explained to teach basic mathematics can be found at:

An online prime factor calculator can be found at:

This also shows how to manually calculate prime factors.