Adding longs strings of positives and negatives

When adding a long string of positives and negatives, such as $(-4)+(+9)+(+4)+(-2)$, there are two very common approaches:

  • Method 1: Find the sum of all the positives, then find the sum of all the negatives, and then add the two answers together.
  • Method 2: Find all the number pairs whose sum is zero. Then add whatever is left over.

Both methods work, but depending on the numbers involved sometimes one method is easier than the other.

 

Example 1: $(-4)+(+9)+(+4)+(-2)=$

Method 1: Collecting "like" signs Method 2: Collecting "opposite" signs

Example 1a

Example 1b

 

Example 2: $(+3)+(-5)+(-9)+(+5)+(-3)=$

Method 1: Collecting "like" signs Method 2: Collecting "opposite" signs

Example 2a

Example 2b

 

 

 

Self-Check


Question 1

Find the sum:

$(-3)+(-7)+(+4)+(+7)+(+3)=$

[show answer]


Question 2

Find the sum:

$(+13)+(-4)+(+7)+(-13)=$

[show answer]


Question 3

Find the sum:

$(-4)+(+9)+(+2)+(-5)=$

[show answer]


 

 

 

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