# 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

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

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)Solve the following subtraction problems without using the number line:

**a.****b.****c.****d.****e.****f.**

Following are the answers to the practice questions:

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.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