Number
Integers
Add and subtract positive and negative whole numbers.
Until now every number you have counted with has been zero or bigger. Integers carry on past zero in the other direction: -1, -2, -3 and so on. Picture a number line with zero in the middle, the positive numbers stretching off to the right and the negative numbers stretching off to the left.
Have a play
Have a wander along the line — nothing here is right or wrong. See how far each number sits from zero, and which side of it.
Tap anywhere on the line.
The one rule to hold on to
Adding moves you to the right. Subtracting moves you to the left. That is true everywhere on the line, whether you start above zero or below it.
Worked example
What is -3 + 5?
Put your finger on -3.
Always start at the first number, not at zero.
Try it together
Now work out -9 + 4 - 6 together.
A long string of integers looks frightening, but you never have to do it all at once. Take it one step at a time, left to right.
1.Deal with the first two only. What is -9 + 4?
Watch out
Two minus signs next to each other undo one another. Taking away a debt leaves you better off, so -10 - (-4) is the same as -10 + 4, which is -6.
Have a go
Have a go on your own: -12 + 20
Hint: Twenty steps right from -12. Twelve of them just get you back to zero.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.