Common Core Standard 1.OA.1.: Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem
Ehow has a great explanation of the different models of subtraction. We have been practicing the completion model, the comparison model and the whole/part/part model (missing part).
The completion model helps students learn that subtraction is the opposite of addition, teaching students to solve an addition problem where one addend is missing, by using a subtraction problem. For example: Jason had 4 stickers. His mom gave him some more. Now he has 6 stickers all together. How many did his mom give him? We could write this problem as the following number sentence 4 + x = 6. Students can use the counting up method to solve this problem by starting at 4, then counting up on their fingers to get to six. They can also use a subtraction expression to solve this problem: 6-4=2. Students must understand that subtraction is the opposite of addition and that if they look at how many there are altogether, then subtract off what he had to start with, they will find the missing addend.
The comparison model uses subtraction when comparing two groups to determine how many more or less either group has. For example: Jason had 4 cookies. Susie had 6 cookies. How many more cookies does Susie have? Students can make a picture to solve this problem:
They can also use a subtraction expression to solve this problem: 6-4=2. Students must understand that if they look at the larger group, and subtract the part that they have in common, they will be left with the difference.
The
part/part/whole model is very similar to the missing addend problem in how it
is solved, but the type of word problem the students will encounter is
different. This problem will involve two parts of a whole that are somehow
different. For example: There are 8 dogs and cats dancing. Four dogs are
dancing. How many cats are dancing? This could also be written as a missing
addend sentence: 4 + x = 8. Students could again use the counting up method, or
can draw a missing addend picture and draw to count up
Just like the completion model, they can also use a subtraction expression to solve this problem: 8 - 4=4. Students must understand that subtraction is the opposite of addition and that if they look at the whole (how many there are altogether), then subtract off how many items are in the first group, they will find out how many items are in the second group.
Our
Common Core standard requires first graders to understand and solve all of
these types of problems. Please discuss and practice these types of problems
with your child and make sure to review their daily work. Below, you will find
some additional subtraction resources that you can use to help your child
practice subtracting.
Videos:
Online Subtraction practice and games:
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