Arithmetic Grade Three

Lesson One hundred thirty-one: Rounding and Dividing

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

Rules for rounding to the nearest 100:

  1. If the number in the tens column is 4 or less round down. Example: 420 -> 400.
  2. If the number in the tens column is 5 or more round up. Example: 450 -> 500.
Rounding and then Dividing:

Here's a sample problem for you: 

     
      Original      	    	Rounded 
       Problem          	Problem

      656 ÷ 7      -->          700 ÷ 7 = 100
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

     812 ÷ 8      -->            800 ÷ 8 = 100

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