standard_description: Find the conjugate of a complex number; use conjugates to find moduli and quotients of complex numbers.
problem_activity: Narrative
In this activity, students continue to use the relationship between multiplication and division to reason about situations that involve division. Students divide three-digit numbers by single-digit divisors and find results with and without a remainder.
Launch
Groups of 2
Activity
5 minutes: independent work time on the first question
2 minutes: partner discussion
2
–
3 minutes: partner work time on the second question
Monitor for students who clearly show how they use partial products or partial quotients to answer the questions.
Student Facing
Jada is writing multiples of a mystery number. After writing a bunch of numbers, she writes out 126.
Mai says 6 is the mystery number.
Priya says 8 is the mystery number.
Andre says 9 could be the mystery number.
Which student do you agree with? Show your reasoning and include equations.
Jada gives one more clue: “If I keep writing multiples, I’ll get to 153.”
What is the mystery number? Explain or show your reasoning.
Student Response
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Activity Synthesis
“How could we use division to help us find out the mystery number?” (If the result has a remainder, then the divisor could not be the mystery number. 153 divided by 6 has 3 as a remainder. 153 divided by 9 has no remainder, so 9 is the mystery number.)


aligns: no