# An Elapsed Time Strategy

This lesson can be used as a pre-lesson for the Beyond Just AdditionLesson plan.

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This lesson can be used as a pre-lesson for the Beyond Just AdditionLesson plan.

Students will be able to use addition strategies in the context of solving elapsed time word problems.

##### Language

Students will be able to explain how to use addition on a number line to solve elapsed time word problems using sentence starters and key vocabulary.

(2 minutes)
• Display an image of a stopwatch and ask students to discuss the purpose of the object.
• Explain that the job of the stopwatch is to keep track of the time that is passing. Define the term Elapsed timeAnd share that you can figure out the time that has passed using other strategies if you do not have a stopwatch available.
• Share the Language Objective for the lesson and have students repeat it. Tell the class that they will be using a number line to solve elapsed time word problems today.
(10 minutes)
• Give each student a Glossary and go over each of the words, definitions, and images as you display the Vocabulary Cards. Ask students to think about any instances in which they have heard the words used in a different situation. Provide additional examples for the vocabulary words as needed to provide more context for learners.
• Tell the class that in maths, there are many ways to arrive at answers. Specifically, there are a few strategies for finding the answer to elapsed time word problems, and they'll focus on using a number line today to solve the problems.
• Display the fourth problem on the Elapsed Time Word Problems 1 worksheet, and have the class choral read the problem. Explain that you will follow a step-by-step procedure to solve the problem and find how long the lunch lasted. Write the following steps on the board or an anchor chart for student reference throughout the remainder of the lesson:
• 1 - Read the word problem and determine the start time and end time.
• 2 - Draw a number line and label the start time at the beginning and the end time at the end.
• 3 - Determine what marks to put on the number line.
• 4 - Jump along the number line from the start time to the end time and count the value of the intervals to determine the elapsed time.
• Model solving the example problem with a number line that starts with 12:00 p.m. and ends with 1:05 p.m. Draw marks in 5 minute intervals on the number line. Think aloud about how to jump along the number line in a way that gets you from the start to end time correctly. Model jumping by fivess, then by tens, and then show them how to jump an hour from 12:00 to 1:00 p.m. and then add the five minutes. Point out that the answer is the same each time, but some strategies were more efficient than others.
• Ask students to turn and talk to a partner about which jumping strategy they liked best and why. Provide a sentence frame, such as "I liked jumping by ____Best because ____."
(8 minutes)
• Have students take out a whiteboard and whiteboard marker. Tell them that they will work together in a small group to solve the following elapsed time word problem:
• I started cooking dinner at 4:10 p.m. I finished cooking at 6:20 p.m. How long did it take for me to cook dinner?
• Provide sentence starters/frames to support student conversation about their process:
• The start/end time is ____.
• We should label the number line with ____.
• The marks should be ____.
• We can jump by ____Intervals because ____.
• The elapsed time is ____.
• Discuss as a class and have students use the sentence starters/frames when sharing how they arrived at their answer.
• Divide students into no more than eight small groups. Give each small group a word problem strip from the Elapsed Time Word Problems 2 worksheet. Instruct small groups to solve the problem on their whiteboards and use the sentence starters/frames to discuss. They should all be prepared to share out with the class about how long the event lasted in their word problem.
• Gather as a class and call on a representative from each small group to share out. Provide feedback and clarification as necessary.
(12 minutes)
• Tell students that they are going to do an oral activity where they explain how to solve an elapsed time word problem using addition on a number line.
• Write the following word problem on the board: "My best friends and I met at the movies at 6:45pm. We were picked up at 8:15pm. How long were we at the movies?"
• Instruct students to take out their maths journals or a blank piece of paper. Have them look at the problem on the board and write down their ideas and reasoning for solving the problem using addition on a number line. Provide a sentence starter for students. For example, "I can solve this by ____." and "I know my answer is correct because. ____." Encourage them to create the visual to assist them in making sense of the explanation.
• Give students time to think about what they will say to the first partner to explain how to solve the problem. Inform them that they will not be able to use their notes for the discussion portion of the activity.
• Put students into partnerships, and instruct each student in the partnership to share their reasoning. Remind them that their goal is to be clear as they explain their strategy. Even if they have the right answer or they both agree, the goal is to be able to clearly explain their thinking to each other. Share that it is acceptable, and even encouraged, to ask clarifying questions during the explanations.
• Scramble the partners and instruct students to repeat the same process. The goal is that they make their reasoning even clearer and stronger.
• Instruct students to return to their seats and look at the response they wrote down at the beginning of the activity in their maths journals or on the blank piece of paper. Instruct them to write down a final explanation in complete sentences. Allow students to use a refined drawing to support their explanations.
• Engage the class in a discussion about their responses to the initial elapsed time word problem, and how their explanations changed throughout the activity. Have students complete the sentence frame, "I used to think ____, but now I think ____."

BEGINNING

• Have learners repeat instructions and key vocabulary to the teacher.
• Supply sentence stems to help students formulate their answers. For example, in the Introduction portion of the lesson use, "A stopwatch is used for ____." In the Assessment portion, "The birthday party lasted for ____." can be used.
• Provide a word bank of key terms and phrases for students to use in group and class discussions.
• Group students intentionally based on academic and language needs.

• Allow learners to utilize glossaries and dictionaries for unfamiliar words.
• Encourage students to answer questions and participate in discussions without referring to the sentence stems or frames for support.
• Choose advanced ELs to share their ideas first in group and class discussions.
• Have learners repeat instructions and key vocabulary, summarizing important information for the class.
• Put students in mixed ability groups so they can offer explanations and provide feedback to beginning ELs when appropriate.
(5 minutes)
• Give each student an index card and have them complete the following word problem using the number line strategy: "The birthday party started at 2:15 p.m. and it ended at 3:30 p.m. How long did the birthday party last?"
• Instruct students to write the answer using a complete sentence because it shows an understanding of what the answer means
(3 minutes)
• Ask students to consider the following questions for a class discussion:
• Do you know of any other strategies for solving elapsed time word problems that do not involve a number line? (Another strategy is ____.)
• How does the number line help you solve elapsed time word problems? (The number line helps me by ____.)
• Remind students that finding elapsed time is a skill that we use in our daily lives, and the number line is a helpful strategy because it provides a visual of the time that passes.

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