How Many Under the Shell

  • How Many Under the Shell?

    Grade: PreK to 2nd

    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?

    Objectives and Standards

    NCTM Standards and Expectations
    • Number and Operations
    • Pre-K - 2
    • Number and Operations