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EL Support Lesson
Solving Elapsed Time Word Problems
Students will be able to subtract time from a given endpoint.
Students will be able to create an elapsed time subtraction word problem to match a number line using sentence starters and key vocabulary.
- Facilitate a Think-Pair-Share by asking students to think about different strategies they use for subtraction. Have them turn and talk to a partner and then share out as a class. Elicit answers that include: draw a picture, count backwards, number lines, count forwards, friends of 10 trick, fact families.
- Tell the class that they will be focusing on a specific strategy for subtraction today as they work with time.
Explicit Instruction/Teacher modeling(8 minutes)
- Draw a blank number line on the board and explain that this strategy will be the focus of today's lesson about elapsed time. Define elapsed time as the amount of time that has passed from the beginning of an event to the end. Use the Vocabulary Cards to teach the other tiered vocabulary words that students will use throughout the lesson. Challenge them to use these words in their explanations and questions they ask today.
- Provide a real-life example about your classroom to help students understand the concept of elapsed time. For example, if the class needs to be at lunch at noon and it takes us five minutes to walk there, what time do we need to leave the classroom?
- Think aloud about the different strategies you could use to figure out the elapsed time in the example word problem (e.g., look at a clock, draw a picture, use the number line). Model using the number line that you drew on the board and label 12:00 p.m. and marks to the left in intervals of five. Show how you can jump back just one time to get to your answer of 11:55 a.m. To support struggling students, use intervals of one minute between each mark and count back by individual minutes.
- Display a copy of the Elapsed Time: Subtraction worksheet on the document camera and read aloud the first word problem. Think aloud about the important information in the word problem that will help you decide how to set up the number line. Say, "I think that 6:15 p.m. is important information because that is the time the event ended. Also, 45 minutes is important because that's how long the event lasted. This problem is asking me to find out when the event started. I'm going to have to count backwards on the number line."
- Draw a number line underneath the word problem on the worksheet, label 6:15 and draw marks to the left with intervals of five. Model counting back by fives on the number line until you have jumped nine times, which is 45 minutes to the left. Explain that the presentation started at 5:30 p.m. because it is 45 minutes before it ended at 6:15 p.m. Point out that it makes better sense for mathematicians to figure out smart intervals so they aren't counting back by ones. Ask students to suggest any other options for intervals on the number line that would have worked in this example.
- Follow the same think aloud procedure for the second problem on the worksheet, using the number line strategy to count back. Be sure to think aloud about how you can decide the best intervals to use.
Guided Practice(12 minutes)
- Distribute the Elapsed Time: Subtraction worksheet to each student and direct them to the third problem. Have the class choral read the problem together. Facilitate a Think-Pair-Share where students first think about the important information in the problem and circle it on their worksheets. Then, have them turn and talk to a partner about what information they think they will use on their number line. Last, share out as a class and provide sentence frames for students, such as "I think ____ is important because ____." and "This will be important for my number line because ____."
- Instruct students to draw a blank number line on their worksheets underneath the word problem. Use student answers from the Think-Pair-Share to guide them in labeling it. (e.g., Say, "I heard someone say that 5:00 p.m. is an important piece of information from the number line and that it should be labeled at the end of the number line.")
- Have volunteers share their thoughts about how to find the answer to the word problem, and invite them to explain their thinking and demonstrate how to jump intervals on the number line.
- Repeat the same procedure with the class for the fourth word problem on the worksheet. This time, have students do more of the talking and explaining while you simply draw the number line, marks, and labels on the displayed teacher copy based on students' instructions. Provide sentence stems/frames to support their explanations:
- To find the elapsed time, we have to ____.
- The intervals should be ____ minutes because ____.
- We have to count forward/backward because ____.
- I start at 5:00 p.m. and ____.
- I know the answer is ____ because ____.
- Tell learners that now they are going to work backwards by first looking at a number line with information on it, but they will not know the word problem. They will think about what the word problem could be. Display a number line with the following specifications:
- The final number on the right is 8:30 p.m.
- Intervals are 10 minutes.
- The beginning number on the left is labeled 7:40 p.m.
- Jumps go from 8:30 p.m. to 7:40 p.m. in the ten minute intervals with an arrow showing the direction.
- Model thinking aloud about the number line, suggesting a scenario. Say, "If this is a number line for an elapsed time word problem, I know that the event ended at 8:30 p.m. because it's the last number on the number line. So I can choose an event, like a birthday party or a show at the zoo. Since I know the end time of the event and I see that the intervals are pointing to the left, it shows I have to count backwards. That tells me that I'm looking for the start time of the event. My problem could be, "We left the birthday party at 8:30 p.m., and we were there for 50 minutes. What time did we get to the party?"
Group work time(10 minutes)
- Tell the class that they are going to see a number line with information on it, and this time they are going to create the story or situation that corresponds to it. Then, they will work with a partner and share their stories. They will ask each other questions for more detail. Then, they will revise their stories by adding details or clarification where needed.
- Give each student a blank sheet of paper on which to write their story.
- Display a number line with the following specifications:
- The final number on the right is 10:30 a.m.
- Intervals are five minutes.
- The beginning number on the left is labeled 9:35 a.m.
- Jumps go from 10:30 a.m. to 9:35 a.m in five minute intervals with an arrow showing the direction.
- Instruct students to take 1-2 minutes to come up with a story or situation that corresponds to the number line.
- Put students into partnerships and have them share their stories. Remind them to ask each other questions or ask for more details. Provide a list of possible questions on the board. For example, "Why did you jump to the left on the number line? How many minutes does that jump represent? Can you explain that again please?"
- Have students revise their stories by adding details or clarification where needed.
- Circulate and identify individuals to share with the whole group. Have them display their word problem on the document camera and share any changes they made to their story. Prompt them by asking questions about how they know their word problem would result in that number line.
- Call on other students to agree or disagree with their peer's explanation. Give them a sentence starter to support them, such as "I agree/disagree that the word problem goes with the number line because ____."
Additional EL adaptations
- Allow access to reference materials in home language (L1).
- Have learners repeat instructions and key vocabulary to the teacher.
- 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.
- Encourage students to keep their Glossary available throughout the lesson in order to utilize the key vocabulary in discussions and explanations.
- Allow learners to utilize glossaries and dictionaries for unfamiliar words.
- Pair students with beginning ELs to offer language support during group work.
- 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.
- Give each student an index card and instruct them to create a word problem for elapsed time and solve it using a number line. For struggling students, provide a number line with labeled intervals for them to use.
Review and closing(3 minutes)
- Pose the following question, "Why does a number line help you solve elapsed time word problems? "
- Challenge them to use the key vocabulary from today's lesson and provide a sentence starter. For example, "A number line helps me solve elapsed time word problems because ____."
- Allow a few students to share out, and remind them that the number line is an important strategy to use as they solve elapsed time word problems because it provides a visual of the numbers.