Adding and subtracting positive and negative numbers

To add and subtract numbers always begin counting from zero.

When adding positive numbers, count to the right.

When subtracting positive numbers, count to the left.

Using a number line

Number line showing negative and positive numbers

Example

Calculate 4 - 5 - 3.

Imagine moving up and down a number line to get to the answer.

Starting from zero, count up to {4}. Then subtract {5}. Then subtract {3}. The answer is {-4}.

Number line showing negative and positive numbers

Number line calculation

Calculate 4 - 5 - 3

Question

Calculate: - 2 + 9 - 10 + 6.

The answer is {3} or {+3}.

Calculating - 2 + 9 - 10 + 6 using a number line

Two signs

  • When adding positive numbers, count to the right.
  • When adding negative numbers, count to the left.
  • When subtracting positive numbers, count to the left.
  • When subtracting negative numbers, count to the right.

Remember:

  • subtract when two different signs appear next to each other
  • add when two of the same signs appear next to each other
Adding and subtracting negative and positive numbers

Example

3 + {-5} = 3 - 5 = -2

3 - {-5} = 3 + 5 = +8 (or {8})

Question

Calculate:

a) 10 + - 7

b) 4 - - 3

a) 10 + - 7 = 10 - 7 = 3

b) 4 - -3 = 4 + 3 = 7