Division terms, factors, primes - 4th grade

In this lesson we have a chart for numbers 1-30, and I check whether each of them is divisible by 1, 2, 3, 4, 5, 6, 7, 8, and 9. The larger numbers didn't fit, but not to worry, our check is sufficient to find all the primes between 1 and 30: they are numbers that are only divisible by 1 and by themselves. Lastly we check whether 79 and 87 are prime or composite numbers, based on divisibility. This lesson is meant for 4th grade math. The first part of the lesson explains the terms factor, multiple, and divisible, and it is found here:

In this lesson we have a chart for numbers 1-30, and I check whether each of them is divisible by 1, 2, 3, 4, 5, 6, 7, 8, and 9. The larger numbers didn't fit, but not to worry, our check is sufficient to find all the primes between 1 and 30: they are numbers that are only divisible by 1 and by themselves. Lastly we check whether 79 and 87 are prime or composite numbers, based on divisibility. This lesson is meant for 4th grade math. The first part of the lesson explains the terms factor, multiple, and divisible, and it is found here:

I explain a systematic way of finding all the factors of a given number. Basically, we check whether numbers 2, 3, 4, 5, and so on are factors of the number, and every time we find a factor, we write the multiplication and write down both factors. Going through the counting numbers in order, at some point you will know that you will have found all the factors, because the large factors will "meet" the small factors. It's much easier to understand by an example so please watch the video. This topic is first encountered in 4th grade math (in Common Core) but may be in some other grade/year in other countries/standards.

I explain a systematic way of finding all the factors of a given number. Basically, we check whether numbers 2, 3, 4, 5, and so on are factors of the number, and every time we find a factor, we write the multiplication and write down both factors. Going through the counting numbers in order, at some point you will know that you will have found all the factors, because the large factors will "meet" the small factors. It's much easier to understand by an example so please watch the video. This topic is first encountered in 4th grade math (in Common Core) but may be in some other grade/year in other countries/standards.

Learn some basic terminology related to numbers and divisibility: What does it mean when one number is factor of another, when a number is a multiple of another, or a number is divisible by another. This lesson is meant for 4th grade math. The second part of the lesson is found at In it, we find out what prime numbers are. :)

Learn some basic terminology related to numbers and divisibility: What does it mean when one number is factor of another, when a number is a multiple of another, or a number is divisible by another. This lesson is meant for 4th grade math. The second part of the lesson is found at In it, we find out what prime numbers are. :)

I explain the terms dividend, divisor, and quotient plus we practice those a little. Then we delve into the problems in division by zero. Instead of just announcing that "You cannot divide by zero", I explain WHY that is. Because of the problems, dividing by zero is "undefined". Lastly we look at zero divided by zero, and why that ends up being "undetermined"... essentially, there could be many possible answers that would work, so 0/0 is termed (by mathematicians) "undetermined". Check out also my other videos for division-related topics at

I explain the terms dividend, divisor, and quotient plus we practice those a little. Then we delve into the problems in division by zero. Instead of just announcing that "You cannot divide by zero", I explain WHY that is. Because of the problems, dividing by zero is "undefined". Lastly we look at zero divided by zero, and why that ends up being "undetermined"... essentially, there could be many possible answers that would work, so 0/0 is termed (by mathematicians) "undetermined". Check out also my other videos for division-related topics at