en.wikipedia.org/wiki/Negative_number

In general, subtraction of a positive number yields the same result as the addition of a negative number of equal magnitude. Thus.

www.khanacademy.org/math/arithmetic/arith-review-negative-numbers/arith-review-sub-neg-intro/v/adding-and-subtracting-negative-number-examples

Learn how to add and subtract negative numbers. The problems solved in this video are 2 - 3 = -1 and -2 - 3 = -5 and -2 + 3 = 1 and 2 - (-3) = 5 and -2 - (-3).

www.khanacademy.org/math/arithmetic/arith-review-negative-numbers/arith-review-sub-neg-intro/e/adding_and_subtracting_negative_numbers

Practice subtracting positive and negative single-digit numbers.

www.khanacademy.org/math/arithmetic/arith-review-negative-numbers/arith-review-sub-neg-intro/a/subtracting-negative-numbers-review

Review the basic of subtracting negative numbers and try some practice problems.

www.wyzant.com/resources/lessons/math/elementary_math/positive_and_negative_numbers/subtracting_positive_and_negative_numbers

Subtracting positive and negative numbers can also be tricky because there are several rules to remember and follow. Rule 1: Subtracting a positive number ...

www.mathsisfun.com/positive-negative-integers.html

add subtract -- goes up. And you can take away weights (you are subtracting negative values). the basket gets pulled upwards (positive) ...

www.purplemath.com/modules/negative2.htm

When you'd subtracted a positive number, you'd moved to the left. Now, if you're adding a negative, you can regard this is pretty much the same as when you ...

www.bbc.co.uk/bitesize/ks3/maths/number/negative_numbers/revision/3

Adding and subtracting. To add and subtract numbers always begin counting from zero. When dealing with positive numbers count to the right. When dealing ...