Number Theory for Grades 4–6
Eight focused skills: factors, primes and composites, prime factorization, divisibility, GCF, LCM, and number-theory challenges.
Browse the skills
Each card opens a parent-readable explanation plus a direct Numeris practice room.
Finding Factors of a Number
A factor of a number is a whole number that divides it evenly, with no remainder.
Practice / Learn →Prime and Composite Numbers
A prime number has exactly two factors: 1 and itself (like 7 — only 1 and 7 divide it).
Practice / Learn →Prime Factorization with Factor Trees
Every whole number greater than 1 can be written as a product of prime numbers — its prime factorization — and there's only one way to do it (order aside).
Practice / Learn →Divisibility Rules
Divisibility rules let you tell whether one number divides another without doing the full division.
Practice / Learn →Greatest Common Factor
The greatest common factor of two numbers is the largest number that divides both.
Practice / Learn →Least Common Multiple
A multiple of a number is what you get by counting by it (multiples of 4: 4, 8, 12, 16…).
Practice / Learn →Number Riddles — Factors, Multiples & Primes
Number riddles combine clues — "I'm a prime number between 10 and 20, and my digits add to 4" — and you use everything you know about factors, multiples, and primes to narrow down the one number that fits every clue.
Practice / Learn →Number Theory Challenge
This capstone mixes everything: a single problem may ask you to factor a number, judge whether it's prime, find a GCF or LCM, and reason from several clues at once.
Practice / Learn →Jump into the interactive rooms.
Use the app for free practice, or open a specific skill from any page.
Want a printable set too?
Get the free Reasonwell sample pack while the math workbook line is coming soon.