Arithmetic Grade Three

Lesson One hundred twenty-five: Rounding and Dividing

Before we get too far into this lesson, let's review a little:

Rules for rounding to the nearest 10:

  1. If the number in the ones column is 4 or less round down. Example: 42 -> 40.
  2. If the number in the ones column is 5 or more round up. Example: 45 -> 50.
Rounding and then Dividing:

Here's a sample problem for you: 

     
      Original      	    	Rounded 
       Problem          	Problem

      66 ÷ 7      -->          70 ÷ 7 = 10
By rounding off the first number we can quickly divide and get an answer which is close to the actual answer. This is a quick way of estimating the real answer.

Here's another example for you: 

     
      Original          	Rounded 
       Problem          	Problem

     82 ÷ 8      -->            80 ÷ 8 = 10

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