All these videos are from the Khan Academy. They cover the concepts of Multiples, Factors and Primes. The explanations are very clear. If you’ve been stuck in this area or need a reminder then watch them.
Finding Factors: The basics
Finding Factors: this video goes over an example how to find all the factors of a number. Watch how systematic Sal is in his approach. It also touches on rules of divisibility and division strategies.
Prime Numbers: ever been stuck on prime numbers, what they are and how to find them. Watch this.
Prime Factorisation: How to find them.