Illustrative Mathematics Grade 4, Unit 1: Factors and Multiples
In this unit, your child begins the year with factors and multiples. They build rectangles from square tiles to find every factor pair of a number, list multiples, and sort numbers up to 100 into prime and composite. It sets up the next unit, where factors and multiples help with equivalent fractions.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 1?
- Building rectangles from square tiles to find every factor pair of a number up to 100, and naming it prime or composite. Learn more about finding factors and multiples up to 100: Finding factors and multiples up to 100 · Learn more about spotting prime numbers
Sample questions to try together
These are real questions from our practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
4 × 9 = 36. Which sentence is true?
- 4 is a multiple of 36.
- 36 is a multiple of 4, but not of 9.
- 36 is a multiple of both 4 and 9.
How you can help
- Lay 30 tiles, crackers, or coins in rectangles on the table. Ask your child to find all four factor pairs, then try 31 and explain why there's only one.
- Clap out multiples on a walk: count by 3s and 4s together, and listen for the numbers you both say, like 12 and 24.
- Ask a planning question: "Can 28 kids line up in equal rows of 3? Of 4? Of 7?" Connect each yes to a factor of 28.
Where kids can get stuck
- Missing a factor pair by not checking every number in order, like skipping 5 × 6 for 30.
- Thinking a bigger number must have more factors, so 31 seems to have more than 12.
- Calling a number a factor when it's a multiple, like saying 30 is a factor of 5.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- factor
- A number that multiplies with another number to make a given number, like 4 in 4 × 6 = 24.
- factor pair
- Two numbers that multiply to make a given number, like 3 and 8 for 24.
- multiple
- The product of a number and a whole number, like 6, 12, and 18 for the number 6.
- prime number
- A number greater than 1 with exactly two factors, 1 and itself, like 7.
- composite number
- A number greater than 1 with more than two factors, like 12.
- array
- Objects arranged in equal rows and columns.
Ready to build your child’s confidence with factor pairs and multiples?
In Bobby's Math Club, your child practices these skills at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free.
Join the club
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
Which math standards does Illustrative Mathematics Grade 4 Unit 1 cover?
Illustrative Mathematics Grade 4 Unit 1 covers this math standard. Each one links to what it means, sample questions, and teaching strategies.
- 4.OA.B.4: Find factors and multiples up to 100, and spot prime numbers.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.