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?

Diagram. One rectangle split into 4 parts. One part labeled question mark. The other 3 parts labeled 8. Total length, 128.
Diagram. One rectangle split into 4 parts. One part labeled b. The other three parts labeled 8. Total length, 128.

Activity 1 Mai’s Beads

Problem 1

Match each diagram with a situation. Explain your reasoning.

1:

Diagram. One rectangle split into 3 parts. One part labeled n. The other two parts labeled 10. Total length, 124.

2:

3:

  1. Mai had 104 beads. She bought two packs of beads and now she has 124 beads. How many beads were in each pack?

  2. 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?

  3. 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

A game called Mancala in progress.

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?

  1. Write an equation to represent the situation. Use a letter for the unknown quantity.

  2. Solve the problem. Explain or show your reasoning.

  3. 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?

  1. Write an equation to represent the situation.  Use a letter for the unknown quantity.

  2. Solve the problem. Explain or show your reasoning.