# Addition and Subtraction Facts

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 −
- 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

A video will appear online shortly to describe how to use the activity in detail.

This activity teaches addition and subtraction facts up to twenty. Addition facts should be learnt

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