Today, I will add three addends to find an unknown sum.
Vocabulary
Teacher Resources
Adding 3 addends: adding together three numbers in an equation.
3 + 3 + 4 = x (unknown) 6 + 4 10 = x
Considerations: This lesson represents a skill that is necessary for mastery of 1.OA.2. Students need to understand that the unknown can be represented by any letter or symbol. Students need to be aware there are multiple ways to solve each problem.
Equations can be written vertically or horizontally.
Drawing
Steps: Solve for the unknown:
3 3 + 4
6 + 4
1. Pick a strategy to add two of the three addends together. 2. Add the sum of those addends to the third addend. 3. Record the sum of all three and solve for the unknown.
/ *MP1: Make sense of the problem and persevere in solving it! *MP8: Find a strategy to help solve the problem. Directions: Solve the addition problems with three addends using counters and drawings.
4+4+3=Y Y=
1.
State the objective: Today, I will add three addends to find an unknown sum.
Identify a 3-addend equation as an equation where 3 numbers need to be added together. The sum is unknown and is represented by a letter or symbol.
Explain that the first step is to pick a strategy to add 2 of the addends. The doubles strategy can be used. Circle both of the 4s, prove by drawing 8 circles, and draw a ^ (or caret) and record the sum of eight.
Model how to draw 3 more circles and count on from the first sum of 8 to add the third addend of 3 until reaching 11.
Record the final sum of 11 as the unknown.
4+4+3=Y 8
Y = 11
(The doubles plus one strategy can also be shown as the first strategy by adding 4 + 3 and then adding 4 more to = 11.)
/ Directions: Solve the addition problems with three addends using counters and drawings.
2.
6 0 + 7
6
=
Restate the objective: Today, I will add three addends to find an unknown sum.
Identify a 3-addend equation as an equation where 3 numbers need to be added together. The sum is unknown and is represented by a letter or symbol.
Explain the first step of picking a strategy to add 2 of the addends. The identity property can be used to add 6 + 0. Circle 6 and 0. Represent 6 and 0 with counters and draw a ^ (or caret). Record the sum of 6.
Model how to use the doubles plus one strategy by representing 7 with counters and solving 6 + 7.
Directions: Solve the addition problems with three addends.
8+1+5=
1.
= 0 8 + 4 X
2.
X=
*MP3: Do you agree/disagree with what
said?
*MP6: How do you know your answers are correct/reasonable?
Recap today’s lesson with one or more of the following MP questions: MP1: What did you do first? Why? MP4: How can you relate this to something in real life? MP8: What strategies did you use to help solve the problems?