Got place value basics? Great! Now, let’s apply those concepts as we go deeper into place value with the idea of more and less!
When thinking about “more or less,” we want students to be able to manipulate the place value strips in a way that helps it make sense. For many students, “more or less” is very confusing. If you ask a student to put their finger on 46 on a hundreds chart and then add 10 or show 10 less, most often, they’ll just start one-to-one corresponding to find their new number (47, 48, 49, 50 and so on), instead of looking for the pattern and going down a column to get to the new number.
Typically, the person who actually goes down the row to get to the new number is actually the teacher, pointing, guiding, whispering until the student gets it right. In actuality, a student may learn the procedure, but not completely understand the idea of adding on that 10 more without counting on because they’d haven’t had the experience. We want to help students become comfortable manipulating numbers in different ways, without really having to give much thought to it.
“More or less,” while we might start it in early first grade, is a very predominantly second grade concept. You might start by having students add on 10 more, and then 20, or 10 or 20 less, then 100 more or 100 less. The video tutorials for this week (FREE for M³ Members, along with the already done-for-you presentation that you can use for virtual instruction or face-to-face) will engage students in five different exercises (based on grade level).
For example, you might have your students build 528 and then add on 10 more. This activity, similarly to the place value basics activities, can be done with students in pairs – one person being in charge of the 100s and the 10s, the other person in charge of the 1s and serving as the Clip Captain. Students have to be able to show the change that’s taking place if you add 10 to the number, so the person in charge of the 10s would bring over an extra 10 and act out the creation of a new number with the place value strips so they can see the overall value.
In our Place Value: More or Less PowerPoint presentations, you’ll find step-by-step instructions for how the students will build the number using concrete manipulatives and adjust it based on what you ask (either adding more or taking away less). We even show some complicated problems where we might stretch over a decade or a century. For example, if we had 592 and we asked kids to add on 10 more, they’d be in the 600s. Trust me, these videos and presentations will show you and your students exactly what that looks like to be able to manipulate that! Remember, they are free for M³ Members! Not a member? Buy the lessons here or click here to become a member today!)
This lesson launch is set up to help kids really understand place value through the use of concrete tools. Students that need the tools will have them readily available, but students that need less structure will be able to use the tools on their own to show how they solved the problem.
More or Less with Decimals
To stretch this concept up into Math4BigKids (upper elementary), we can look at applying the “more or less” idea to decimals. Do your students know what to do when they have .4 and need to add on .3? Do they know that 10 tenths is equal to one whole? You can ask students to show you 10 more or 10 less within hundredths or even into the thousandths place. Helping our big kids manipulate their number to build the mystery number we’re asking for is fun, and you can stretch it even more to include more than just 10 more or 10 less. Depending on the student’s level, you could take it up to 100 more or 100 less, etc.
Some students might just be able to do the arithmetic in their head to add or take away 10, but if they aren’t able to explain why they got their answer, they don’t really understand the concept. This becomes especially important when students advance in the area of decimals. Students could simultaneously build their numbers with the place value discs so they relate the quantity to what they’re doing with the place value strips.