Learning how to find the unknown number in addition and subtraction equations is a first grade, Common Core math skill: 1.OA.8. Below we show two videos that demonstrate this standard. Then, we provide a breakdown of the specific steps in the videos to help you teach your class.
Your students should be familiar with comparing the number of objects within two groups to determine whether the groups are equal. They should also be able to compare two numbers (between 1 and 10) and decide if they are equal (K.CC.6-7).
Understanding equations and addition and subtraction will help your students understand principles later on in first grade as well as in second grade. Your students will be able to think about inequalities, continuing to use their understanding of the equal sign (1.NBT.4).
Later in the second grade, your students will be able to write equations that express equivalent groups and use even numbers, equal parts, skip counting, etc. (2.OA.3-4). They will also be able to write equations to solve word problems (2.OA.1).
Common Core Standard: 1.OA.8 - Determine the unknown whole number in an addition or subtraction equation relating three whole numbers
Students who understand this principle can:
2 Videos to Help You Teach Common Core Standard: List Standard
Below we provide and breakdown two videos to help you teach your students this standard.
Video 1: Finding the Missing Balloons
This video begins by explaining what a missing part in an equation is. It uses a “part-part-whole” chart, which has the total on top and the two numbers which add to equal that number underneath.
The chart shows the equation 4 + __ = 10. The video then gives a word problem that matches the problem: “I got 10 balloons at the fair. 4 of the balloons were green. The rest were red. How many were red?”
The video then gives another word problem for your students to try on their own: “My little sister got 3 pink balloons at the fair. Then she got some more yellow balloons! Now she has 5 balloons in all. How many are yellow?”
All the methods are reviewed before the video ends.
Video 2: Learning how to Find Unknown Numbers
The video reviews that addition and subtraction are related. It uses the equation 7 + 5 = 12, stating that 7, 5, and 12 are part of a fact family. You can create another addition statement and two subtraction statements using these numbers: 5 + 7 = 12; 12 - 7 = 5; and 12 - 5 = 7.
The video explains that by understanding how fact families work, finding an unknown number is possible. A few practice examples are shown to help your students find the unknown number.
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