Different Signs
Part of the Numbers & Operations section of Coddy's Pre-Algebra journey. Lesson 19 of 60.
What is -12 + 5? Start at -12 and walk 5 steps right. You stop at -7, still below zero. The quick way: the signs differ, so subtract the sizes, 12 - 5 is 7, and keep the sign of the number further from zero. -12 is further out than 5, so the answer is -7.
It works the other way round too. 9 + (-4): the sizes give 9 - 4, which is 5, and 9 is further from zero than -4, so the answer is positive 5.
Why subtract? A positive and a negative pull in opposite directions, so they cancel as far as they can. What is left over belongs to the bigger one. With money: you have 5 dollars and owe 12, so after paying what you can, you still owe 7.
Challenge
Work out -17 + 11.
Try it yourself
Simplify the expression
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Numbers & Operations
1Working on the Board
Your First AnswerType the Next LineOne Line at a TimeDots and BarsFriendly ProductsRecap: Board Work4Adding Integers
Adding Two NegativesDifferent SignsZero PairsAdding Several IntegersRecap: Adding Integers2Order of Operations
Multiply Before AddingLeft to RightParentheses FirstBrackets Inside BracketsThe Fraction Bar GroupsRecap: Order of Operations5Subtracting Integers
Add the OppositeSubtracting a NegativePlus and Minus in a RowDistance Between NumbersRecap: Subtracting Integers