How to tell if a 2 digit number is PRIME in 1 SECOND! | FUN Number Theory!

We explain a simple mental math trick to decide if a two digit number is prime instantaneously! We first prove (and explain) a basic statement (in number theory) on prime factors of two digit numbers, in an accessible way. We then explain divisibility tests by 2, 3, 5, and 7. Finally, we give some random two digit numbers, and explain how to instantaneously decide if they are prime numbers.

The video is designed for people at all levels of math who know what prime numbers are, and are familiar with some basic algebra and divisibility rules (by small numbers like 2, 3 and 5). For example, this video would be interesting also to students interested in math puzzles, creative math tricks, competition math, math olympiads, math proofs, number theory etc.

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