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DB-34

Class Introduction 15 min

Have blocks, holders, and number lines displayed.Show the problem:

16 + 27

How can we use these materials to solve this problem? Have students discuss materials they would use and

how they would use them.

Have the students share their thoughts aboutwhether the sum will be more or less than 30.

It seems that most of us agree that the sum will be more than

30. But there are lots of numbers that are more than 30! Does

anyone have an idea about what the exact answer will be? We

call this a prediction.

Have volunteers describe and demonstrate their

strategies for the class to observe.

Make sure students strategies include using one ortwo number lines to show the counting-on view ofaddition. (See figure.) Children might choose to:

Place blocks on the number line up to thenumber 16, then continue to place more blocks,counting on 27 more. They determine the sumby reading the final number. (Note: They canseparate the two addends with a strip of tagboard to show the two parts.)

Line up 16 blocks on one number line, and 27

on a second. Slide the 27 blocks onto the firstnumber line and determine the sum.

Have students model the problem in the place valueview (that is, using packed blocks) as well:

Students show each addend with blocks-of-10and singles on the place value mat. Next theycombine the two quantities, pack as muchas possible, and set the digit cards to show 4blocks-of-10 and 3 singles.

Ask,What do you notice about the sums? Are they the same even

though you used different strategies? Is this a coincidence?

Were we just lucky?

Why are they the same? If we add two different numbers in two

different ways again, do you think well get the same answer or

different answers?

Explain that mathematicians often solve problems indifferent ways to check their answers.

tenshundreds ones

tenshundreds ones

3

61

164327

+

72

Slide the blocks to join.

Number Line:

Packing:

Unit 4Activity A Two Ways To Add

7/28/2019 Two Ways to Add

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7/28/2019 Two Ways to Add

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ACTIVITY

SH

EET

DB-36 Unit 4Activity A Two Ways To Add

Two Ways To Add

Partners:

Which way will you add?

o Number Line

o Packing

Which way will you add now?

o Number Line

o Packing

&

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=4.

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=2.

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Partners:

Which way will you add?

o Number Line

o Packing

Which way will you add now?

o Number Line

o Packing

&

=1.

=2.

=3.

=4.

=1.

=2.

=3.

=4.

Name______________

Student Book p. 17