Comparing quantities to 20
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Students learn to compare amounts from 11 to 20 and know when an amount is more or less.
Show the image of the watermelons on the interactive whiteboard and ask the class if they know how many watermelons there are.
Show a selection of quantities on the interactive whiteboard and tell students that they don't always need to count to know which amount has more or less. Sometimes you can just see it right away. If you can't see the difference right away you count the objects. Use the number line to 20. Using the number line you can see which number is bigger or smaller by its position on the number line. Also, show the students that there are different ways of counting. Sometimes the rows are in fives, sometimes tens, and that using skip counting (5s or 10s) can help speed up their counting. Compare a few numbers as a class and emphasize that you can count in different ways (including skip counting).
Check that students can compare amounts to 20 by asking the following questions:
- When is one quantity more than another quantity?
- How do you know when one amount has more or less than the other?
Students first practice indicating more or less with numbers ordered in a 5 or 10 structure. Next, they practice with the question of if there are enough objects to share with the children.
Discuss again that it is important to be able to compare quantities. That way they know who has more legos. Check that students know that sometimes you don't have to count to know if a quantity is more or less. If you can't see which has more or less right away, you need to count. Use the number line to see which number comes first on the number line, and which comes after. Check that students have understood by showing the image of cookies and students on the interactive whiteboard. Have students figure out if there are enough cookies for the students. Encourage them to explain that they used skip counting in 5s to count and the number line to compare amounts.
Students who have difficulty comparing amounts can practice the number line to 20. Also, encourage them to draw a line between the students and the objects, so they have visual support.
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