## How Many Under the Shell?

Grade:

Pre-K-2

Standards:

Math Content:

Number and Operations

After Okta hides some bubbles under a shell, he
then either adds more bubbles or takes some away. Students have to determine how
many bubbles are left under the shell.

At the Set Up screen, choose either a number or
Random to determine how many bubbles to start with; then, choose addition,
subtraction, or both. If you choose nothing, the number of bubbles will be
randomly chosen, and you'll receive a mix of addition and subtraction problems.

Hit **Start** to go to the problems page.

Okta will show you some bubbles, hide them under the shell, and then either add some or take some away. When Okta asks, "How many bubbles are under the shell?" enter your answer using the keypad.

If you need to see the demonstration again, click **Replay**. For a
different problem, click **New**. To select new parameters, click the **Set
Up** arrow.

At the Set Up screen, select the number

**5**and choose**–**(subtraction). This will give you subtraction problems that start with five bubbles. Then hit**Start**.You will be given a problem that looks like this: 5 – __ = __. (The number in the first blank will be filled in, but you'll need to find the number for the second blank.)

- What can you say about the two numbers that go in the blanks?