## Chapter 12

### Part 1: Home and School Investigation

Send the Letter to Family (PDF file) home with each child. Once all of the children have brought in their groups of 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, just put the children with different partners.

### Part 2: Be an Investigator

A good time to do this investigation is after Lesson 6 on subtracting two-digit numbers.

#### Materials

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

#### Introducing the Investigation

Give each child an Investigator Worksheet. Tell them that they are going to do an activity where they count the number of jumps they can do.

#### Doing the Investigation

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

Now do the same activity for 15 seconds. Have the children guess how many jumps they can make in 15 seconds and write it on their worksheets. Ask them if they think they will make more or fewer jumps in 15 seconds than in 30 seconds. Then let the children jump as you use a watch to time 15 seconds. Have the children write down the actual number of jumps they made in their tables.

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

#### Extending the Investigation

Ask the children to predict how many jumps they can make in five seconds and then time them jumping so they can find out. Have them find the difference between the number of jumps they can do in five seconds and the number of jumps they can do in 30 seconds.