This activity helps teach addition and subtraction facts up to twenty. These facts should be learned by pupils so they can be recalled quickly.

## Using the activity

When you start the activity ten penguins are on the first iceberg and none on the second. The addition fact 10 + 0 = 10 is displayed. Click the move right button and a penguin will jump on to the second iceberg. Notice also that the addition fact has changed to 9 + 1 = 10, click the button again and another penguin will move. The addition fact is now 8 + 2 =10, so hopefully pupils can start to appreciated that the first number can be found by counting all the penguins on the first iceberg and the second number is the count on the second iceberg. You can probably guess that the left-arrow moves penguins the other way.

The activity is about connecting the visual picture of the penguins with the formal mathematical writing of the number fact. So various parts of the interface can be hidden, click on the numbers and the will turn over to leave a '?' . Click on the first cloud button and a cloud will move in to cover the penguins. Same thing happens when clicking the second cloud. You can create a random problem by clicking the dice, the clouds will move in and the numbers flip to '?' . So you can now reveal certain parts, for example turn over the first number card and ask the pupils what it means. Hopefully they will correctly say that it tells how many penguins are on the first iceberg. So obviously there are many ways this can be done.

## Editing totals and the number line

The arrow buttons can change the positions of penguins, but not the total. To do this click the edit button, two slider controls will appear. The total slider is the top one, the second represents the number on the first iceberg. Click and drag the sliders and you will see the penguins instantly update to match the values.

The activity can display a number line by clicking the line button now the pupils can see how to represent the addition fact on the line.

## Subtraction Facts

To change addition facts to subtraction facts click the iceberg button. Now the second iceberg moves off screen and any penguins on board will jump off into water. Now the arrows will move the penguins in and out of the water. Some other things happen are

• The + sign flips to a â
• The total in the addition sum (the last number) swaps with the first number
• The number line representation changes with a red arc traveling back from the original total
To hide how many are swimming, click the water button, this changes the transparency so the penguins become invisible. Clicking the dice will automatically do this in subtraction mode, so again the pupils can try and work out the problem depending on the bits the teacher chooses to reveal.

This activity teaches addition and subtraction facts up to twenty. Addition facts should be learnt so that recall is fast

This activity develops strategies for

• Counting two sets to find a total
• Counting on from the first number
• e.g. if know the first number count on the second number for the total

The activity also helps to develop key concepts such as

• addition is commutative, that is the two numbers can be added in any order
• to recognize subtraction is the inverse of addition
• to understand complementary sums in order to work out the difference between two numbers
left
Move a penguin to the first iceberg
right
Move a penguin from the first iceberg
Iceberg
Toggle the display of the second iceberg, this changes mode between addition and subtraction
Fog1
Click to toggle the cloud of fog blocking the first iceberg
Sea
Click to toggle the transparency of the water, this will show or hide swimming penguins
Fog 2
Click to toggle the cloud of fog blocking the second iceberg
total
Move this slider to set the total number of penguins
left-berg
Move this slider to set the total number of penguins on the left iceberg
Random
Click the dice, the clouds will move in and a random penguin problem created
number line
Click to toggle the display of the number line
slider controls
Click to display the slider controls to change total or penguins on first iceberg