Plus and Minus in a Row
Part of the Numbers & Operations section of Coddy's Pre-Algebra journey. Lesson 25 of 60.
When two signs meet, merge them into one. Two of the same sign make a plus; two different signs make a minus. So 8 - (-3) is 8 + 3, which is 11, while 8 + (-3) is 8 - 3, which is 5.
Why? A minus sign means 'the opposite of'. One minus flips the direction of a move, and a second minus flips it back. In 8 + (-3) there is only one flip, so the move goes left. In 8 - (-3) there are two, so it goes right.
Merging first turns every problem into one you already know. -8 - (-3) becomes -8 + 3: different signs, so subtract the sizes and keep the sign of -8. The answer is -5.
Challenge
Work out 2 - (-5) and -4 - (-1), then mark both answers on the number line.
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
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