Lesson 3 — Activity 3: Dividing Whole Numbers


Getting Ready


What is division? Think of division as a series of subtractions.


This problem concerns shopping for T-shirts. Here is an example:

Justin paid $40 for several T-shirts on sale for $10 each. How many did he buy?

  • One way to solve this problem is to subtract 10 from 40 until you reach 0, then count how many times you subtracted $10.

  • $40 – 10 – 10 – 10 – 10 = 0

  • A quicker method is to divide the total cost ($40) by the cost per item ($10).

    $40 ÷ $10 = 4 T-shirts

Try This:


This problem concerns having enough cookies to share with friends.

Chad made 48 cookies to share with 12 friends. How many cookies will each friend receive?

Choose the method you'd like to solve.



48 – 12 – 12 – 12 – 12 = 0

48 ÷ 12 = 4




Addition and Subtraction

Just as subtraction is the opposite of addition, division is the opposite of multiplication.

Each multiplication fact also gives a division fact for the same grouping:


4 x 4 = 16             

16 ÷ 4 = 4

 Image 1
2 x 8 = 16
8 x 2 = 16

16 ÷ 2 = 8
16 ÷ 8 = 2

 Image 2
3 x 5 = 15
5 x 3 = 15

15 ÷ 3 = 5
15 ÷ 5 = 3

 Image 3
Multiplication and Division

Knowing your multiplication facts is very helpful when performing division. If you know that 4 x 5 = 20, then you know that 20 ÷ 4 = 5.

If you have some trouble recalling the facts, remember to use the multiplication table from L3 — A2.



Many strategies can be used to divide larger numbers, such as using:
 
  • base 10 blocks (manipulatives) Base ten blocks are used to solve many math problems.


  • estimating and calculating by using paper and pencil


  • checking, by using a calculator 


Click here to watch a video to see the strategies that can be used to divide.



It may be a little scary to think about dividing by two or more digits, but really, it is just a matter of following the same steps as when dividing by one digit. There are a couple of things that can be done to help.



Now click here to watch this video demonstration that shows how easy this can be if you use rounding to help reach a solution.




In the video, the person rounded to the nearest whole number, but pointed out two important things to note:


1. When you multiply the divisor by the number you have entered into the quotient, the answer MUST be SMALLER than the number you were dividing into. If it isn't, you won't be able to complete the next step, which is to subtract. If this is the case, go down a number.


2. When you have subtracted, the answer must be smaller than the divisor. If this is the case, go up a number.


Images courtesy of www.imagesgoogle.com

Try This:


Work through these division questions. You will notice in each question that you are expected to do more of the steps by yourself.

Replace each * with the correct answer. If you are unsure, review the videos above to help you. Use the pause button so you can go step by step.


Division practise 1
Division practise 2
Image 3
Image 4

  
Division practise 5



Click here to find extra practice questions on division. Answers are supplied!