standard_description: Solve two-step word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding. (This standard is limited to problems posed with whole numbers and having whole number answers; students should know how to perform operations in the conventional order when there are no parentheses to specify a particular order (Order of Operations).)
problem_activity: Narrative
The purpose of this activity is for students to practice rounding to the nearest ten and hundred in context. Students work with numbers from a previous lesson to estimate the total number of students in a school. They learn that how you round (to the nearest ten or hundred) can give different estimates for the same situation.
Launch
Groups of 2
“Let’s revisit the number of students in different areas in a school. We’re going to use rounding to help Andre and Lin make an estimate of the number of people in the whole school. Andre plans to round the numbers to the nearest hundred. Lin plans to round them to the nearest ten.”
“Make a prediction: Whose estimate is going to be greater? Be prepared to explain your reasoning.”
30 seconds: quiet think time
Share responses.
Activity
“Work with your partner to complete the table and the last problem.”
7–10 minutes: partner work time
Student Facing
The table shows the numbers of people in different parts of a school at noon during a school day.
Andre and Lin are trying to estimate the number of people in the whole school. Andre plans to round the numbers to the nearest hundred. Lin plans to round them to the nearest ten.
Make a prediction: Whose estimate is going to be greater? Explain your reasoning.
Work with a partner to find Andre and Lin’s estimates. Record them in the table. Then find the totals.
|  location  | number | Andre's estimate                       (nearest hundred) | Lin's estimate                       (nearest ten) |
|------------|--------|----------------------------------------------------------|----------------------------------------------------|
| playground |   94   |                                                          |                                                    |
| cafeteria  |  163   |                                                          |                                                    |
|  art room  |   36   |                                                          |                                                    |
|  library   |   13   |                                                          |                                                    |
| classrooms |  216   |                                                          |                                                    |
| gymnasium  |  109   |                                                          |                                                    |
| music room |   52   |                                                          |                                                    |
|   total    |        |                                                          |                                                    |
Make two observations about the completed table. Was your prediction correct?
Student Response
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Activity Synthesis
Invite students to share their observations about the completed table, including whether it matched their predictions.
“When we are estimating a total, rounding to the nearest ten or the nearest hundred can give us different results. If you were rounding to estimate a total, would you round to the nearest ten or nearest hundred?” (The nearest ten because you get an estimate that’s closer to the total. The nearest hundred because multiples of 100 are easier to work with.)
“Keep these ideas in mind as you use rounding to estimate in future lessons.”


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