# Multiplication and division

Contents

Multiplying and dividing positive and negative whole numbers, understanding place value, and rounding numbers.

## Concept of multiplication and division

Let's introduce ourselves to two of the most fundamental ideas in all of mathematics: multiplication and division!

3:33

Intro to multiplication

Sal uses arrays and repeated addition to visualize multiplication.

4:19

Multiplication as groups of objects

Sal uses arrays to show different ways to multiply and get the same solution.

5:29

More ways to multiply

Sal uses arrays and repeated addition to multiply.

8:01

The idea of division

Sal uses an array and understanding of multiplication to divide.

## Basic multiplication

If 3 kids each have two robot possums, how many total robot possums do we have?
You liked addition, but now you're ready to go to the next level. Depending on how you view it, multiplication is about repeated addition or scaling a number or seeing what number you get when you have another number multiple times. If that last sentence made little sense, you might enjoy this tutorial.

1:20

Number line 1

Exercise

Whole numbers on the number line

Practice skip counting to find a number on a number line with only two tick marks labeled.

13:20

Basic multiplication

Introduction to multiplication

Exercise

Multiply 1-digit numbers

Multiply two 1-digit numbers. Some problems include multiplying by 10.

15:27

Multiplication 2: The multiplication tables

Introduction to the multiplication tables from 2-9.

3:03

Example: Ways to represent multiplication

Multiplying Whole Numbers and Applications 1

12:11

Multiplication 3: 10,11,12 times tables

Multiplication 3: Learning to multiply 10, 11, and 12.

## One-digit division

Every time you split your avocado harvest with your 10 pet robot possums, you've been dividing. You don't farm avocados? You only have 8 robot possums? No worries. I'm sure you've divided as well.
Multiplication is awesome, but you're ready for the next step. Division is the art of trying to split things into equal groups. Like subtraction undoes addition, division also undoes multiplication. After this tutorial, you'll have a basic understanding of all of the core operations in arithmetic!

17:02

Division 1

Introduction to division

Exercise

Basic division

Divide two numbers. Quotients are equal to or less than 10.

Exercise

1-digit division

Divide two numbers. Quotients are equal to or less than 10.

2:28

Example: Expressing division in multiple ways

Dividing Whole Numbers and Applications 1

## Starter multiplication and division word problems

Math is super useful in the real world. In this tutorial, we'll get some practice figuring out things that would have been tough without the powerful tools of multiplication and division!

2:17

Comparing with multiplication: basics

Sal solves multiplication comparison problems.

Exercise

Compare with multiplication

Rewrite multiplication equations as comparisons and comparisons as equations.

2:39

Comparing with multiplication: age

Sal solves a multiplication comparison word problem.

2:32

Multiplication word problem example 1

1:48

Division word problem example 1

1:10

Comparing with multiplication: magic

Sal solves a multiplication comparison word problem with Harry Potter characters.

Exercise

Multiplication and division word problems

Practice solving multiplication and division word problems. Some problems have remainders.

## Multi-digit multiplication

You know your multiplication tables and are ready to learn how to multiply *any* number (actually, any whole number). Imagine the possibilities! This tutorial will make you unstoppable.

3:05

Multiplying by multiples of 10

Sal decomposes multiples of ten to multiply.

Exercise

Multiply by tens

Multiply a 1-digit number by a multiple of 10.

1:51

Multiplying: 2-digit by 1-digit

Sal solves 32x3.

1:54

Multiplying: 3-digit by 1-digit

Sal solves 4x201.

Exercise

Multiply without regrouping

Multiply 2- or 3-digit numbers by 1-digit numbers. No regrouping.

2:09

Multiplying: 2-digit by 1-digit (regrouping)

Sal solves 6x37.

2:15

Multiplying: 3-digit by 1-digit (regrouping)

Sal multiplies 7x253.

3:24

Multiplying: 4-digit by 1-digit (regrouping)

Sal multiplies 9x8085.

Exercise

Multiply with regrouping

Multiply 3- or 4-digit numbers by 1-digit numbers. Regrouping (carrying) needed.

11:15

2-digit times a 2-digit number

Multiplying a 2-digit number times a 2-digit number

3:18

Example: 2-digit times 2-digit

Multiplying Whole Numbers and Applications 2

Exercise

Multiply 2-digit numbers

Multiply 2-digit numbers by 2-digit numbers. Regrouping (carrying) needed.

10:27

Multiplying multiple digit numbers

Sal multiplies 2- and 3-digit numbers using "standard algorithm".

Exercise

Multi-digit multiplication

Multiply 2-3 digits by 3-4 digits with carrying.

1:51

Multiplication estimation example

Estimating the product of two, 2-digit numbers

6:17

Multiplication 7: Old video giving more examples

2 examples of multiplying a 3 digit number times a 2 digit number. 1 example of multiplying a 3 digit number times a 3 digit number.

## Loooong division!

You know your multiplication tables and are getting the hang of basic division. In this tutorial, we will journey into the world of loooong division (sometimes, referred to as "long division", but that's not as much fun to say).
After this tutorial, you'll be able to divide any whole number by any other. The fun will not stop!

11:39

Introduction to long division

Dividing into larger numbers. Introduction to long division without remainders

Exercise

Divide by 1-digit numbers (no remainders)

Practice dividing 2- and 3-digit numbers by a 1-digit number.

3:45

Intro to remainders

Sal shows how a remainder is what's left over in a division problem.

2:41

Long division with remainders: 3771÷8

Sal divides 3771÷8 with long division.

10:07

Long division with remainders: 2292÷4

Sal divides 2292÷4 and 1,735,092÷3 with long division.

Exercise

Divide with remainders

Practice finding remainders in division problems, like 247÷5.

2:49

Dividing by 2-digits: 7182÷42

Sal divides 7182÷42. There is no remainder.

Exercise

Division by 2-digits

Divide 3-digit and 4-digit numbers by a 2-digit number without remainders.

Exercise

Multi-digit division

Practice dividing multi-digit whole numbers. These problems use remainders.

9:35

Level 4 division

Dividing a two digit number into a larger number

## Lattice multiplication

Tired of "standard multiplication". In this tutorial we'll explore a different way. Not only is lattice multiplication interesting, it'll help us appreciate that there are many ways to do things. We'll also try to grasp why it works in the first place. Enjoy!

7:15

Lattice multiplication

Introduction to lattice multiplication

8:21

Why lattice multiplication works

Understanding why lattice multiplication works

## Partial quotient division

Feeling constrained by traditional long division? Want to impress your friends, family and even your enemies? Well, partial quotient division may be for you (or it might not). This very optional tutorial will show you that there are many ways to slice a walnut (just made up that colloquialism).

8:27

Partial quotient method of division

An alternate to traditional long division

7:56

Partial quotient method of division 2

Another example of doing long division using the partial quotient method

## Fancy multiplication and division word problems

In this tutorial, we'll start to challenge you with more sophisticated multiplication and division word problems.
If you understand mult-digit multiplication and long division, you have all the tools you need to tackle these.
May the force be with you!

2:59

Division word problem: field goals

Sal solves a division word problem.

2:38

Multiplication word problem: pizza

Sal solves a multiplication word problem.

2:10

Multiplication, division word problems: pedaling how fast?

Using multiplication and division to make estimates. Easy? Maybe, but what's more important is that you try.

## Area models and multiplication

Most of us learn to multiply eventually, but only a select-few actually understand what the multiplication represents. This tutorial, with the help of area models, will allow you to be part of this elite group.

4:58

Multiplying with area model: 78 x 65

Sal uses an area model to multiply 78x65.

8:47

Multiplying with area model: 16 x 27

Sal uses an area model to multiply 16x27.

Exercise

Multiply 2-digits numbers with area models

Use an area model to decompose factors and multiply.