Round Up or Down?
Lesson 2 of 3
Objective: SWBAT apply their understanding of place value to round numbers to the nearest ten
Today I want to start with a little competition and the teams will be boys vs. girls. I’m going to need 1 boy and 1 girl to help with the first problem! You need to add these numbers in your head, and the first one who knows the answer will get the point.
I have 3 math problems written on the board, but each is covered. On one side, I intentionally have rounded numbers (100 + 20) and on the other side I have the original numbers, not rounded (ex: 154 + 37). We repeat this process for all 3 problems and the same team should always get the rounded numbers.
I noticed that the girls won every round, why do you guys think that happened? Here I expect students to say the numbers were easier, they all ended in zero and similar responses.
Today I want to teach you one way that 3rd graders can round numbers to make them easier to work with! You’re going to need this very important song to help you remember, “5 or more, raise the score! 4 or less, let it rest!” We repeat this song a few times, so all students are getting practice.
Here I draw 2 visual examples, one of a number line and one of hill, to illustrate how numbers that have 5 or more round up and 4 or less round down. I always present a variety of ways of looking at the numbers or the concept so that students have different ways available to process it. It's also important for me to emphasize that there is not just 1 right way of doing things, and that we all show our work in various ways and that's ok.
If I have the numbers 44 and 73 (I write the numbers), how can I set up my problems to find out how to round them?
We set up both numbers on a number line, and a hill, to illustrate how we can round each one. I do a few more examples to illustrate the concept. We repeat the song each time so students start to remember the “rules of rounding”. Students must be able to use a model to show where a number falls and which ten it will be rounded to (MP5).
I made these rounding boards for you to use today, and we’re going to stick with our tens so we can become experts before we move on to our 100’s. I have this pile of number cards for you to use, and you can create any numbers you want with the cards you pull, as long as you stick to 2 digit numbers each turn! I want you to show your work with both your number line and rounding hill so that you become an expert using both ways and can pick which one works better for you.
The rounding board is just a legal size piece of paper with 1 box in the center for students to place their number. On each side a line extends out with lines where they can write in their numbers that surround the number cards in dry erase marker.
Check for Understanding
You have one last job for today. I need each of you to show me what you learned by rounding this number, using both of your rounding tools you learned today, on your note card.
I write the number 37 on the board and expect students to use both the hill and the number line to round the number to 40. I collect their exit ticket on their way out the door to see which students are able to round the number correctly, and which students will need a small group tomorrow to reinforce the concept. Exit tickets are a quick way to see which students mastered the concept for the day and which will need additional work.