Rounding rules for estimating

Several people have asked over the years about ROUNDING when estimating the result of a math problem. I finally wrote something to put online so I can refer people to that when they ask... 

 
It seems to be a confusing topic! But really, in a nutshell, there are no exact rules.
When estimating...
 
  1. Consider your mental math skills. Round as little as possible, based on what YOU can calculate in your head.

  2. And, consider also how the rounding up or down will affect the final result. Sometimes it is better to round one number up and the other down, even though the technical rounding rules would dictate otherwise.

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