Positive Negative Numbers Adding and Subtracting Whats The

Positive & Negative Numbers. Adding and Subtracting.

What’s The Missing Number ? This is a revision of number facts you already know. Complete (1) – 6 + 18 = 12 (2) -13 + 10 = – 3 (3) 12 – 34 = – 22 (4) -11 – 14 = – 25 (5) 22 – 39 = – 17

Some New Rules. What happens if you add a negative number ? Consider the sum below : 6+ – 4 = Rule 1 : Adding a negative number is just the same as taking away that number. Hence: 6 – 4 = 2 Is the same sum The same rule applies for taking away a positive. 5–+8= Is the same as 5 – 8 = – 3

Subtracting A Negative Number. Five judges have to give a score of between – 10 and 10 in a ball throwing competition. Here are the judges scores. – 4 – 7 6 Add up the total score : 3 – 2 – 4 The rules say that the lowest score is always removed. What score is this ? – 7 6 – 2 – 4 3 Now add up the new total: 3

Consider the sum below : Old score Minus lowest score Equals new score. Put the numbers in place of the statements: – 4 – – 7 = 3 That is to say : – 4–( – 7)=3 Which is the same as : – 4+7 =3

Rule 2 : Subtracting a negative is the same as adding the number on. What a dastardly good rule !!

Some Worked Examples. Calculate : ( 1) 6 + - 7 = 6 – 7 = -1 ( 2) 4 - - 9 = 4 + 9 = 13 ( 3) -3 + - 7 = -3 – 7 = -10 ( 4) 2 - + 5 = 2 – 5 = -3 ( 5) -7 - - 7 = -7 + 7 = 0

What Goes In The Box ? Is the same as : ( 1) – 5 + – 6 = – 5– 6= -11 (2) 6 + – 4 = 6– 4= 2 (3) 8 – – 7 = 8+7= 15 – 3– 8= -11 12 + 6 = 18 (4) – 3 – + 8 = (5) 12 – (– 6 ) =