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Cogito

Grade 2 Math · Chapter 4 · Lesson 4

Practice Worksheet

Explaining Why It Works

Say what you did and why it was allowed.

10 problems · about 12 minutes · 2.NBT.B.9

NameDate

Figure — use these to answer the problems

Say out loud what happens to the rods and what happens to the cubes.
First number
and Second number
Altogether

Tens

7

Ones

13

47 + 36 = 83

First number47
Second number36
Figure 1

Warm-Up Review

From earlier lessons. Loosen up before the new work.

3 problems

  1. From “Adding Past 100”

    58 + 67 = ?

    Answer

  2. From “Making a New Ten”

    29 + 34 = ?

    Answer

  3. From “Adding With Place Value”

    23 + 41 = ?

    Answer

Warm Up

Straightforward practice. Get the method working first.

3 problems

  1. Someone says the bundled ten is "a one". Are they right?

    • No. It is one ten.
    • Yes. It is a one.

  2. 56 + 38 = ?

    Answer

  3. Why do you add the tens to the tens?

    • Because they are the same size unit.
    • Because they are on the left.

Build It Up

The same ideas with more to keep track of.

1 problem

  1. 48 + 27 = ?

    Answer

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

3 problems

  1. In 48 + 27, how many loose ones are there before bundling?

    Answer

  2. Spot the Mistake

    Someone works out 34 + 25 and gets 95. What went wrong?

    • They added a ten to a one.
    • Nothing. 95 is correct.

  3. Why Bundle?

    Why is it allowed to swap ten ones for one ten?

    • They are worth the same amount.
    • It looks tidier.