Estimation Strategies

We have currently wrapped up addition and subtraction with estimation, which includes using "compatible numbers" and "rounding". This is often a tricky concept for our students because we are working with big numbers and finding approximate solutions are abstract. Here's a summary of what we're learning...

--We looked at when to estimate (if we don't need an exact answer; instead I just need the answer that is "about" or "approximately").
--We also looked at how to round using the idea of number lines (the number you are rounding is close to what 10 or what 100 on a number line).
--We also used "compatible numbers", which is when I get to change the numbers up a bit to be easier to add and subtract. For example, for 346-137, I might simply change the numbers to be 347-137 because this makes it an easy problem to subtract. Compatible numbers are nice to use because you can often easily find the real answer. We can also use the same concept when finding exact solutions.
--Lastly, if the problem calls for estimation, I encourage students to not solve for the real answer and then round it because in real life if I knew the answer, I would not round it...I would say the exact answer. Rounding is supposed to be used to find a close answer in an easier way, so I should not find the exact answer. Instead, they need to round their number and then add or subtract. They can find the real answer if they want to check, but remember that these problems are long, so doing that much work usually frustrates students.



Here's a look at a "rounding hills" strategy that can help students understand how to round. We relate this to a number line.