Subtraction Help

1
Subtraction Help

• By Valerie Brunton
• December 7, 2004

2
Four Methods

• There are four different ways to think about
  subtraction
• These four ways are
• Take-away
• Comparison
• Missing addend
• Number line

3
Take-away

• For the take-away method, you take the number you
  are subtracting away from the other number.
• An easy way to do this is to
• Make a circle.
• Then put the same number of Xs in that circle as
  the first number.
• Next, draw a small circle around the same amount
  of Xs as the second number (the one youre
  subtracting).
• Lastly, take that smaller circle out of the
  larger one and count the number of Xs that are
  left in the large circle.
• Example for 5-32
• xxx xxx
• xx

4
Comparison

• The comparison method is kind of like the
  take-away one.
• For this one you
• Draw two separate circles to start off with.
• Then fill the first one in with the same number
  of Xs as the first number from the problem.
• Fill the second circle with the same number of
  Xs as the second number.
• Next, draw lines connecting each X in the first
  circle to one and only one X in the second
  circle.
• There should be some left over Xs in the first
  circle that do not have pairs in the second one.
  Count up how many of the leftovers there are and
  that is the answer.
• Example for 4-22
• x x
• x x
• x
• x

5
Missing Addend

• The missing addend method can be a little tricky
  sometimes.
• To complete a subtraction problem using this, you
  have to
• Write the problem horizontally (one number on top
  of the other).
• Draw a box underneath the equals line where the
  answer belongs.
• Now, think about the addition you know. Come up
  with a number that when its added to the bottom
  number will equal the top one.
• Put that number into the box. That is your
  answer.
• Example for 10-64
• 10
• - 6
• 4 4610

6
Number Line

• The number line method is the fourth way you can
  think about how to subtract one number from
  another.
• To use this one you must
• Draw a number line, making sure both the numbers
  and all those in between are shown on it. Start
  the number line with the number 0.
• Start at the first number and draw an arrow back
  to the second number.
• Count how many numbers are to the left of where
  the arrow ends. That number will be your answer
  to the subtraction problem.
• Example for 10-55
• 01 23 45 67 8910

7
Practice

• Now you can practice using all these different
  way of subtracting.
• Here are links to a practice worksheet and
  answers to the worksheet available in PDF format
• Subtraction Worksheet
• Subtraction Worksheet Answers