Adding and Subtracting Multiples of Ten

We are steadily working our way through mental addition and subtraction.  I really like these units because they give students the opportunity to solve problems in different ways and makes them explain their thinking.

Today's math skill was focusing on adding (and I included subtracting) multiples of ten.  Problems like 45 +30, 67 - 20 or (gasp!) 265 + 20... Most of us do pretty well at this - but we definitely needed to solidify the concept a little more so we took today to make sure everyone was on the same page.

We started by reviewing counting by 10's starting in the tens, then moved to starting with any 2-digit number.  I divided my kiddos into 4 groups, each group sitting together in one area of the rug.  I started by rolling the big foam dice cubes (always a hit!) to create a 2-digit number. 

Then we started counting up by 10's.  I pointed at one group, and they started the counting.  After a few numbers, I would clap and point to a different group.  It was their job to pick up the counting from where the other group left off.  This really helped everyone stay engaged and focused because you never knew when I was going to clap and point to another group!  We did this with a few different numbers counting by 10's going forward, then we switched it to counting backwards by 10's. 

(At first everyone in the smaller groups counted in unison, but then after a few rounds they had to each count individually going around their smaller circles, until I clapped and switched to a different group. Doing it this way gave everyone a chance to warm up and feel successful counting together, and switching to counting individually gave me a clear idea of who still needed a little work.)

Now that we were warmed up, we reviewed adding and subtracting multiples of ten.  I wrote a problem on the board and we discussed different strategies for solving it.  Most of my kiddos felt comfortable just subtracting or adding the tens, but some preferred to count up or back to get their answer.  Both ways worked, so everyone's strategy was validated.  After a couple of those, it was on to some fun!

We played a math version of the getting-to-know-game "Find Someone Who Has."  In this game, everyone has a sheet with a number on the top.  That is THEIR number.  Students walked around the room trying to find someone with a number that matched one of their boxes.  When they did (there was at least 1 of each answer, sometimes 2), they wrote that person's name and the answer in the box.

It was a hit!  I heard lots of thinking aloud as students figured out which numbers to look for.  It was fun to see the different ways my kiddos went about the activity, too.  Some started with the first box, answered all the problems and then looked for people who had those numbers.  Some solved one problem at a time.  I even had a couple students who looked at other people's numbers first, then tried to figure out which box to put the number in. (You can find the games in my TpT store HERE, or by clicking the picture.)

We ended our math time with a little independent follow-up activity.  Students worked on their own to roll 2 (or 3) dice, make a number, spin the spinner and write and solve the resulting problem.  This gave me one more chance to see who still might need some help with this concept.

(You can grab the spinner activity freebie HERE, or by clicking the picture.)  The different activities gave everyone a chance to review and practice in a different way and by the end of the math time I knew exactly where everyone stood with this skill.  I was able to differentiate for my learners by using 2 or 3-digit numbers - and by allowing students to use base ten blocks to solve the problems, if needed.

Simple, but effective and fun, too - what more could you ask for?

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