A quick way to estimate the difference of two numbers is to round each number and
then subtract the rounded numbers. {See this previous post for help on rounding.} More often than naught, this won't be the exact answer but it
may be close enough for some purposes. Students need this mental math not only for future math classes and math procedures, but it is also an excellent life skill. Do you have enough money for all your groceries? Did the cashier give you the right amount of change back? When you relate math to MONEY, even eight year old ears perk up! Problem solving extends to all aspects of their world.
Once your students have a strong foundation of rounding, you can move on to estimating the difference. Estimation is a powerful mathematical mental tool to be used both in solving problems and in checking the answer to see if it is reasonable.
Tips to introduce your lesson...
How to estimate a difference by rounding:
How to estimate a difference by rounding:
- Round each number in the problem.
- Subtract the rounded numbers together, mental math is even better.
- Check to see if you have about enough money to pay for your meal at restaurant before you order. Lobster or hamburger?
- Get a ball park idea to double check your answer to a problem. Is 300 an intelligent answer for 992 - 682?
Once you're done with your lesson, I have a variety of resources to help with your spiral review, use them in your math centers, small group lessons, seat work, partner work, the possibilities are endless!
Math Center
Color By Numbers
Task Cards
Task Cards Also Come With an Easy to Print Black and White Version... Perfect for Colored Paper.
This Task Card Resource Also Includes an
Answer Key / Student Self Checking Sheet!
Today's Lesson:
Use any of the links below to read more...
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