Decimals

UK Secondary (7-11)

Add or subtract negative numbers with decimals

Lesson

In Order is Important, we looked at how to solve decimals problems with various combinations of operations. Now we are going to use and extend that knowledge by looking at questions that involve negative decimals.

Remember there are rules for when you add, subtract, multiply or divide with negative numbers.

When you're adding or subtracting:

- if you have adjacent positive (plus) and negative (minus) signs (e.g. $6+\left(-4\right)$6+(−4)), this will become a
**minus sign**. - if you have two adjacent negative (minus) signs (e.g. $2-\left(-5.1\right)$2−(−5.1), this will become
**an addition sign**.

**Evaluate:** $3.4+\left(-5.2\right)$3.4+(−5.2)

**Think:** A **positive** and a **negative** sign together become a **negative**.

**Do:** $3.4+\left(-5.2\right)$3.4+(−5.2) is the same as $3.4-5.2$3.4−5.2.

$3.4+\left(-5.2\right)=-1.8$3.4+(−5.2)=−1.8

Evaluate $8.5+\left(-4.1\right)$8.5+(−4.1).

Evaluate $-9.3-\left(-2.2\right)$−9.3−(−2.2)