Negative Numbers (Cambridge (CIE) IGCSE Maths)

Negative Numbers

What are the rules for calculations with negative numbers?

• When multiplying and dividing with negative numbers

  • Two numbers with the same sign make a positive

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  • Two numbers with different signs make a negative

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• When adding and subtracting with negative numbers

  • Subtracting a negative number is the same as adding the positive

    • e.g. 

  • Adding a negative number is the same as subtracting the positive

    • e.g. 

Where are negative numbers used in real-life?

• Temperature is a common context for negative numbers

  • If the temperature is 3°C, and it cools by 5°C, the new temperature will be -2°C

    • This is equivalent to 3 - 5 = - 2

  • If the temperature is -4°C, and it warms up by 6°C, the new temperature will be 2°C

    • This is equivalent to (-4) + 6 = 2

  • To explain why (-5) - (-6) = 1, you could think of it as follows:

    • A room is -5°C, then -6°C of cold air is 'removed'

    • The room now warms to 1°C

• Money and debt is another common context for negative numbers

  • A negative sign means you owe money

  • If someone has a debt of $200, and they borrow another $400, their total debt is now $600

    • This is equivalent to (-200) + (-400) = -600

  • If someone is in debt by $300, but then pays off $200 of their debt, they are now only $100 in debt

    • This is equivalent to (-300) + 200 = -100