Arithmetic Grade Four

Lesson Fifty-Three: Estimation, Rounding, and Division

One way to estimate the answer to a division problem is to round off the numbers and then divide. Here's an example: 

     ORIGINAL PROBLEM:	3588 / 6 = ?
     
     ROUNDED PROBLEM:	3600 / 6 = ?
As you can see, finding the exact answer to the first problem would be much more difficult than finding the exact answer to the second problem. But finding the answer to the second problem will give you an answer that is pretty close to the answer for the original problem. Therefore, the answer to the second problem will be a pretty good estimation of the first problem.

Here's another example: 


    ORIGINAL PROBLEM: 	7213 / 8 = ?

    ROUNDED PROBLEM:	7200 / 8 = ?
So, again we rounded the first number to the nearest hundred and then we divided. The answer to the second problem will be a pretty good estimation of the answer to the first problem. 

   ROUNDING TO NEAREST 100:

     Remember that when rounding to the nearest 100, if the
     last two digits of the number you are rounding are 50
     or greater you round up. If the last two digits are
     49 or less you round down. 

     EXAMPLES:
 
         4444   --->  4400
     
         5950   --->  6000

         2101   --->  2100

         3349   --->  3300

You get to try a few for yourself on the next page.

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