Introduction to prime numbers - 4th/5th grade math
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.
See also
Remainder in division-related word problems — video lesson
Math Mammoth Division 2 — a workbook with worksheets and lessons for long division, remainder, factors, and primes
Math Mammoth Grade 4 curriculum