Rounding, Estimating & Addition/Subtraction

This week we have been learning about how to round numbers, use this understanding to estimate sums and differences, and we have been practicing addition & subtraction of larger numbers. Here is the lesson we learned about rounding, which students seemed to have a good grasp of.

Rounding - Strong Arms and Weaklings

We also learned to use this information to estimate when performing operations. I tell students to estimate to the largest place value in a number to tell if their answer is reasonable or note. For example:

23,456--->20,000

+ 12,398--->10,000   

                 30,000

So, I would expect my answer to be around 30,000 in this example. If I got an answer of 300, I would know that I have done something wrong somewhere and need to go back and check. 

Finally, we have been practicing adding and subtracting larger numbers. This is something that students should be familiar with from previous grades, but serves as a good reminder. We are practicing adding numbers up to the millions, and then checking our work both by using estimation, and by using subtraction. Students generally are good at addition and subtraction, but often forget to borrow (or regroup) when subtracting. We will be continuing to practice this tomorrow as well.