The Other Side of Zero

Numbers below zero: placing integers on the number line, comparing them, and adding and subtracting with lifts, temperatures and money.

Key ideas

• Integers are …, −3, −2, −1, 0, 1, 2, 3, …; numbers to the right on the number line are bigger.
• Among negative numbers, the one closer to zero is bigger: −1 is more than −7.
• A number and its opposite add to zero: 5 + (−5) = 0.
• Adding a negative number moves left; adding a positive number moves right.
• Subtracting a number is the same as adding its opposite: 3 − (−4) = 3 + 4 = 7.
• Real uses: floors below ground, temperatures below 0 °C, money owed in a bank account.

Remember

Watch out

• Saying −7 is bigger than −1.
• Forgetting that subtracting a negative makes the answer bigger.
• Ignoring the sign when finding the difference between two temperatures.

Worked example