Lesson 9

The purpose of this lesson is for students to use their understanding of place value to solve number riddles.

In this lesson, students use their understanding of place value to determine a secret number and justify why the number matches the clues. When students solve the riddles, they have opportunities to look for and make use of the base-ten structure of numbers (MP7). In the synthesis, students discuss and solve a number riddle.

If students need additional support with the concepts in this lesson, refer back to Unit 4, Section B in the curriculum materials.

For the lesson synthesis, create a chart with clues. Leave a few lines in between each clue. Fold the chart paper so that only the first clue is showing.

• My number has more than 6 tens.
• My number is less than 100.
• My number has 8 tens.
• My number is the sum of \(51 + 32\).

• Create enough riddles from the Number Riddle Cards so each group of 2 students can have a different riddle. Fold the gray cards. Place each set of clues in a bag or envelope and label based on the letter of the riddle.

As you finish up this unit, reflect on the norms and activities that have supported each student in learning math. List ways you have seen each student grow as a young mathematician throughout this work.