Lesson 20 Situations and Equations
Let’s represent and solve problems.
Warm-up Notice and Wonder: The Unknown
What do you notice? What do you wonder?
Activity 1 Mai’s Beads
Problem 1
Match each diagram with a situation. Explain your reasoning.
1:
2:
3:
Mai had 104 beads. She bought two packs of beads and now she has 124 beads. How many beads were in each pack?
Mai had some beads. She bought 2 more packs of beads and each pack has 10 beads in it. Now she has 124 beads. How many beads did Mai have before?
Mai had 104 beads. She bought 2 more packs of beads and each pack has 10 beads in it. How many beads does she have now?
Problem 2
Match each equation with a letter for the unknown quantity to a situation in Problem 1.
Activity 2 Represent, Solve, Explain
Kiran is setting up a game of mancala. He has a jar of 104 stones.
From the jar, he takes 3 stones for 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.
Practice Problem
Problem 1
There are 240 connecting cubes in the box. Five students each take 9 connecting cubes from the box. How many connecting cubes are left in the box?
Write an equation to represent the situation. Use a letter for the unknown quantity.
Solve the problem. Explain or show your reasoning.