Make a Big Difference
Students will be able to fluently round and estimate the differences between three-digit numbers.
- Write the following digits on the board: 4, 6, 9, and 1.
- Ask students to work with a partner to arrange them into two, two-digit numbers and then find the difference between them.
- Have students share out their differences.
- Now ask students to rearrange the digits so that the difference is larger than it was in the first round.
- Ask for a show of hands to indicate who was able to arrive at a larger difference. Have them share some of their strategies. Note how students used estimation thinking as they strategized.
- Note their strategies on a piece of chart paper or on the whiteboard.
Explicit Instruction/Teacher modeling(10 minutes)
- Extend the game to one more round, this time telling students that the group that makes the largest difference wins.
- Determine which groups found the largest difference.
- Have students explain what strategies they used that didn't work. Which ones did work? Revisit your chart of strategies to ensure that they are all represented.
Guided Practice(10 minutes)
- Select a student volunteer to roll three dice. Write the three digits on the board.
- Have another student roll the three dice and write those digits on the board.
- Instruct students to work in pairs to manipulate each of the three groups of digits into numbers that have the highest possible difference.
- Have pairs share out their strategies before sharing their totals. This will help them focus on how they used estimation and other number sense strategizing in their thinking.
Independent working time(20 minutes)
- Assign students to pairs, quickly create a team name, then match each pair with another pair.
- Have students make a T-chart on a blank paper and put team names at the top, one on each side.
- Distribute at least three dice to each group of four, along with scratch paper for them to record their numbers and calculate.
- Instruct student pairs to roll the three dice two times, one for each number, then find the difference. Have them record their difference in their column and find their new total, rotating teams until each team of two has had five turns.
- The team with the largest difference wins.
- Play another round with a new team. This time students arrange the digits and then round each number to the tens or hundreds (their choice) before calculating the difference.
- Have student pairs begin by finding the difference between two-digit numbers then move to three-digit numbers.
- Have groups find the smallest differences.
- Increase numbers to four or more digits.
- Roll the dice and write the three digits on the board. Then do it again. Have students rearrange the numbers and then round each one to the nearest hundred or ten. Then find the difference. Spot check student work.
Review and closing(5 minutes)
- Discuss, "Is it better to round to the nearest hundred or ten in this game?"