Back to Edexcel Number (F) Home
1.1 L) Subtracting & Adding Negative Numbers

Here are the rules when two signs are next to one another:

From these rules, we can see that two signs of the same result in addition; this is the case for + + and - -. Also, opposite signs result in subtraction; this was the case for - + and + -.  
 
Let’s have a few examples.

---

Example 1 
Complete the calculation:

We are taking away a negative number, which means that we are adding 3. 

​The answer to this question is 11. 

---

Example 2 
Complete the calculation:

We are adding a negative number. Opposite signs result in a negative sign. The calculation becomes:

​The answer is 15. 

---

Example 3 
Complete the calculation:

We are adding a positive and we know that signs that are the same become a positive. Therefore, the calculation becomes:

​Therefore, the answer to this question is 78. 

---

Example 4 
Complete the calculation:

We are taking a positive and as the signs are opposite, it results in a negative. The calculation is:

The start number is a negative (-24). Therefore, it is probably best to sketch a quick number line with -24 on it. My sketch is given below.

We are taking 4 away, which means that we are moving 4 towards the left. 

​The answer for this calculation is -28. 

---

End Note
The key rules to remember from this section is that:

• Two of the same signs result in addition; this is the case for + + and - -
• Opposite signs result in subtraction; this was the case for - + and + -

 
It is worth getting these rules down on a revision card.