Combining Signed Numbers Adding and subtracting signed numbers

Combining Signed Numbers Adding and subtracting signed numbers

Step 1: Collapse signs Sometimes you’ll see two signs in a row: 5 + ( -2 ) or 7 – ( -5 ) Collapse them into a single sign using the rule: if the signs are the same, make a single + if the signs are different, make a single – 5 + ( -2 ) = 5 - 2 and 7–(-5)=7+5

Step 2: Combine the numbers Once each number has only one sign, combine them using the following rules: if the signs are the same, ADD if the signs are different, SUBTRACT

Step 3: Determine the sign of the answer The sign of the larger number (just the ‘number’ part – forget the signs for a second) goes on the answer BIG sign wins!

A rule to remember If the first number is positive, it doesn’t have to show its sign. All of the other numbers do have to show their signs. 5– 2+3 5 is positive ~ 2 is negative ~ 3 is positive

Example 1: 5+(+2) Collapse the 2 signs in a row: 5+(+2) 5+2 Signs are the same therefore +

Example 1: Really 5+(+2) 5+2 +5+2 The signs are the same, ADD the number parts 5 plus 2 = 7

Example 1: 5+(+2) +5+2 5 plus 2 = 7 BIG sign wins! Sign of the 5 goes on the answer: + 7

Example 2: 5+(-2) Collapse the 2 signs in a row: 5+(-2)= 5 -2 The signs are different, therefore -

Example 2: Really 5+(-2) 5 -2 +5 -2 Signs different, SUBTRACT the number parts 5 minus 2 = 3

Example 2: 5+(-2) +5 -2 5 minus 2 = 3 BIG sign wins! Sign of the 5 goes on the answer: + 3

Example 3: -5+(+2) Collapse the 2 signs in a row: -5+(+2)= 5+2 The signs are the same, therefore +

Example 3: -5+(+2) -5+2 Signs different, SUBTRACT the number parts 5 minus 2 = 3

Example 3: -5+(+2) -5+2 5 minus 2 = 3 BIG sign wins! Sign of the 5 goes on the answer: - 3

REMEMBER THE RULES Collapse your signs same + different - Decide whether to add or subtract same + different - Sign of the larger goes on the answer (BIG sign wins)