4 Important Sets of Numbers
Parentheses and Powers in the Order of Operations
How to Find Square Numbers

How to Subtract with Negative Numbers

Subtracting a negative number is the same as adding a positive number — that is, go up on the number line. This rule works regardless of whether you start with a positive number or a negative number.

When subtracting a negative number, remember that the two back-to-back minus signs cancel each other out, leaving you with a plus sign. (Kind of like when you insist you can’t not laugh at your friends, because they’re really pretty ridiculous; the two negatives mean you have to laugh, which is a positive statement.)

Math books often put parentheses around the negative number you’re subtracting so the signs don’t run together, so 3 – –5 is the same as 3 – (–5).

When taking a negative number minus a positive number, drop both minus signs and add the two numbers as if they were both positive; then attach a minus sign to the result.

Sample question

  1. Use the number line to subtract –1 – 4.

    –5. On the number line, –1 – 4 means start at –1, down 4, which brings you to –5.

Practice questions

  1. Use the number line to solve the following subtraction problems:

    a. –3 – 4
    b. 5 – (–3)
    c. –1 – (–8)
    d. –2 – 4
    e. –4 – 2
    f. –6 – (–10)
  2. Solve the following subtraction problems without using the number line:

    a. 17 – (–26)
    b. –21 – 45
    c. –42 – (–88)
    d. –67 – 91
    e. 75 – (–49)
    f. –150 – (–79)

Following are the answers to the practice questions:

  1. Subtraction problems

    a. –3 – 4 = –7. Start at –3, down 4.
    b. 5 – (–3) = 8. Start at 5, up 3.
    c. –1 – (–8) = 7. Start at –1, up 8.
    d. –2 – 4 = –6. Start at –2, down 4.
    e. –4 – 2 = –6. Start at –4, down 2.
    f. –6 – (–10) = 4. Start at –6, up 10.
  2. Subtraction problems without the number line

    a. 17 – (–26) = 43. Cancel the adjacent minus signs to turn the problem into addition:
    17 – (–26) = 17 + 26 = 43
    b. –21 – 45 = –66. Drop the signs, add the numbers, and negate the result:
    21 + 45 = 66, so –21 – 45 = –66
    c. –42 – (–88) = 46. Cancel the adjacent minus signs to turn the problem into addition:
    –42 – (–88) = –42 + 88
    Now switch around the numbers (with their signs) to turn the problem back into subtraction:
    88 – 42 = 46
    d. –67 – 91 = –158. Drop the signs, add the numbers, and negate the result:
    67 + 91 = 158, so –67 – 91 = –158
    e. 75 – (–49) = 124. Cancel the adjacent minus signs to turn the problem into addition:
    75 – (–49) = 75 + 49 = 124
    f. –150 – (–79) = –71. Cancel the adjacent minus signs to turn the problem into addition:
    –150 – (–79) = –150 + 79
    Now switch around the numbers (with their signs) to turn the problem back into subtraction:
    79 – 150 = –71
  • Add a Comment
  • Print
  • Share
blog comments powered by Disqus
Calculating Area and Volume for Household Projects
How to Add Large Numbers Using Column Addition
How to Multiply Multiple Digits
Multiplication and Division with Negative Numbers
How to Divide Big Numbers with Long Division
Advertisement

Inside Dummies.com