Step 1: The Basics
Mrs Brown has 5 apples sitting on a table, Mr Brown takes away2 how many are left?
We can tell this problem is a subtraction question beacuse we see the words "takes away". You may also see "minus" "reduces" or of course the word "Subtract".The first step in any subtraction is to find what the question is really asking. In the above question the usefull information is in bold. We then write this problem in mathmatical noteation "5-2". The answer to this question is three as you will be able to see in the pictures below but without actually having any apples how do we get the answer? The next steps show three basic teqniques which will boost confidence until you feel you can do subtraction in your head.
Step 2: Basic Teqnique 1
Step 3: Basic Tequnique 2
Step 4: Basic Teqnique 3
For this technique we will do 10-14
Raise as many fingers as the number you are subtracting from, in this case 10. Now count to 14 each time lowering a finger. When you have no fingers left , make a mental note and start raising them again until you have finished counting to 14. In our example you will have gone to 0 fingers and now have 4 fingers raised. Because you went to zero fingers the fingers still up represent negative numbers. This is no drama just be sure to put a subtract sign in front of the number four as your answer. If you never go to zero fingers the answer will be a regular positive number. If you can tell straight off that 14 >10 (14 is greater than 10) and therefore that the answer will be a negative number just count up from ten to 14 raising a finger each time (rember that answers will be negative). This technique only works for numbers being subtracted from below 10 and answers above negative 10 but once mastered will make more difficult steps later in the Instructable easier.
Step 5: Pen and Paper Method
If the number you are subtracting in a particular column is larger than the one being subtracted from, reduce the number to the left of the number being subtracted from by 1, and add that 1, as 10, to the number being subtracted from then continue to subtract the number being subtracted (quite a scentence I know but it should be clear in the example below).This is called borrowing. This method meas you only have to know how to subract numbers below 20 and you can subtract enourmous numbers from one another. To briefley explain the below example 4-6 gives a negative result so we "borrow" a ten from the 30 to the left of the 4 reducing the 3 to a 2. 14-6 is 8 so we write 8 bellow the 4-6 column then we do 2-2=0 and write that below that column. The number at the bottom is then 08 and sure enough thts the right answer.
Step 6: Algerbraic Subtraction
x-x= 0 Any term subtract itself is zero
x-y =bleurgg You cannot subtract two different terms from one another. You can't take two pears from three apples
xy-y does not =x let y be 4 and x be 3 12-4 is not the same as 3
x-x does not =x either
2x-x = x When terms are all the same just ignore the "x"s until the end and then when giving your answer stick an x after it. If there is no number in front of a term it is a 1 (in this case 2-1=1)