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Negative number operations help students work with values below zero, such as temperatures, elevations, debts, and points lost in a game. This cheat sheet gives quick rules for adding, subtracting, multiplying, and dividing integers. It is useful because sign mistakes are common when students first learn how positive and negative numbers interact. A clear reference helps students check their steps and build confidence. The most important ideas are the number line, absolute value, and sign rules. Adding numbers with the same sign keeps the sign, while adding numbers with different signs uses subtraction of absolute values. Subtracting a number means adding its opposite, so ab=a+(b)a - b = a + (-b). For multiplication and division, same signs make a positive result and different signs make a negative result.

Key Facts

  • A negative number is less than 00 and is written with a minus sign, such as 6-6.
  • The absolute value a|a| is the distance from aa to 00 on the number line, so 8=8|-8| = 8.
  • When adding integers with the same sign, add the absolute values and keep the sign, such as 4+(7)=11-4 + (-7) = -11.
  • When adding integers with different signs, subtract the smaller absolute value from the larger absolute value and use the sign of the number with the larger absolute value.
  • Subtracting an integer means adding its opposite, so ab=a+(b)a - b = a + (-b).
  • The product of two numbers with the same sign is positive, so (3)(5)=15(-3)(-5) = 15.
  • The product or quotient of two numbers with different signs is negative, so 18÷3=6-18 \div 3 = -6.
  • Use order of operations with negative numbers: parentheses first, then exponents, then multiplication and division, then addition and subtraction.

Vocabulary

Integer
An integer is a whole number, its opposite, or 00, such as 3-3, 00, or 77.
Negative Number
A negative number is a number less than 00 and is located to the left of 00 on a number line.
Opposite
The opposite of a number is the number the same distance from 00 on the other side, such as 55 and 5-5.
Absolute Value
Absolute value is a number’s distance from 00, written as a|a|.
Additive Inverse
An additive inverse is a number that adds with another number to make 00, so a+(a)=0a + (-a) = 0.
Sign
The sign tells whether a number is positive or negative.

Common Mistakes to Avoid

  • Treating 4+(6)-4 + (-6) as 22 is wrong because two negative addends combine to make a more negative sum, so 4+(6)=10-4 + (-6) = -10.
  • Forgetting to change subtraction into adding the opposite is wrong because 7(3)7 - (-3) means 7+37 + 3, not 737 - 3.
  • Assuming every answer with negative numbers is negative is wrong because same signs in multiplication or division give a positive result, such as (2)(8)=16(-2)(-8) = 16.
  • Ignoring absolute value when comparing negatives is wrong because a larger absolute value can mean a smaller number, so 9<4-9 < -4.
  • Doing operations out of order is wrong because 3+2×(5)-3 + 2 \times (-5) must multiply first, giving 3+(10)=13-3 + (-10) = -13.

Practice Questions

  1. 1 Evaluate 12+7-12 + 7.
  2. 2 Evaluate 9(4)9 - (-4).
  3. 3 Evaluate (6)(3)+8÷(2)(-6)(-3) + 8 \div (-2).
  4. 4 Explain why 15-15 is less than 5-5 even though 1515 is greater than 55.