Unit 3, Lesson 19
Situations and Equations
Grade 3
Warm-up
Notice and Wonder: The Unknown
What do you notice? What do you wonder?
Activity 1
Mai’s Beads
In this problem, each situation has an unknown quantity. In the diagrams and in the equations, each unknown quantity is represented by the letter n.
Part A
Match each diagram with a situation. Be ready to explain your reasoning.
- Situation 1: Mai had 104 beads. She buys 2 packs of beads. Now she has 124 beads. How many beads were in each pack?
- Situation 2: Mai had some beads. She buys 2 packs of beads. Each pack has 10 beads in it. Now she has 124 beads. How many beads did Mai have before she bought the packs?
- Situation 3: Mai had 104 beads. She buys 2 packs of beads. Each pack has 10 beads in it. How many beads does Mai have now?
Part B
Match each equation with a situation in Part A.
Activity 2
Represent, Solve, Explain
Kiran is setting up a game of mancala (mahn-KAH-lah). He has a jar of 122 stones.
From the jar, he takes 3 stones to put in each of the 6 pits on his side of the board.
How many stones are in the jar now?
- Write an equation to represent the situation. Use a letter for the unknown quantity.
- Solve the problem. Explain or show your reasoning.
- Explain how you know your answer makes sense.
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