## Chapter 22

### Part 1: Home and School Investigation

Send the Letter to Family (PDF file) home with each child. Once all the children have brought in their objects, put the children in pairs. Tell the children to find out how many objects each of them has. After they have done that, have them find the difference in the number of objects in each group. If you want to repeat the activity, have the children change partners. A good time to do this activity is after Lesson 5 on two-digit subtraction practice.

### Part 2: Be an Investigator

A good time to do this investigation is after Lesson 5 on two-digit subtraction practice.

#### Materials

- Investigator Worksheet (PDF file)
- watch with a second hand

#### Introducing the Investigation

Give each child an Investigator Worksheet. Tell them that they are going to do an activity that involves counting handclaps.

#### Doing the Investigation

Ask, *How many handclaps do you think you can do in 30 seconds or a half of a minute?* Let the children make guesses. Use a watch with a second hand to time 30 seconds, and tell the children when to start clapping and when to stop. You might want to put the children in pairs so they can help each other keep track of the handclaps. If you do this, you will need to do two 30-second hand-clapping periods. When the children are finished, tell them to write down in the Investigator Worksheet the actual number of handclaps each of them made.

Now do the same activity for 15 seconds. Have the children guess how many handclaps they can make in 15 seconds. Ask them if they think they will make more or fewer handclaps in 15 seconds than in 30 seconds. Then let the children clap hands as you use a watch to time 15 seconds. Have the children write down in the Investigator Worksheet the actual number of handclaps each of them made.

Finally, ask the children to find the difference between the number of handclaps they made in 30 seconds and the number of handclaps they made in 15 seconds.

#### Extending the Investigation

Ask the children to predict how many handclaps they can make in 10 seconds, and then time them clapping hands so they can find out. Have them find the difference between the number of handclaps they can do in 10 seconds and the number of handclaps they can do in 30 seconds.