Get There On Time: Elapsed Time Word Problem Strategies
Students will be able to subtract time from a given endpoint.
- Ask students if their families are ever late to gatherings or events.
- Call on a few students to share family stories.
- Ask students to think about how you can plan to be on time - take suggestions (i.e. plan ahead, prepare things the night before, leave earlier, etc.).
- Tell students that if they learn to count time backwards, they can use that skill to plan a timely arrival.
Explicit Instruction/Teacher modeling(10 minutes)
- Provide the following fictitious example: The class needs to be at a baseball game in your town at 3:30. If they need to eat snack, wash their hands, make a bathroom stop, clean up the classroom, pack their backpacks, and walk to the performance, when should they start getting ready? (Adjust this example to make it more realistic for your class.)
- On the board, make a table with those things that need to be done before leaving and then discuss and note how much time each will take (i.e. eat lunch 20 minutes, wash hands five minutes, bathroom break five minutes, etc.).
- Draw an open number line on the board and mark 3:30 on the right hand side with the label, 'game starts.' For each activity that must be done, jump to the left on the number line, subtracting the time and write the new time at the stopping point. For example, if it takes 20 minutes to walk to the game, jump to the left from 3:30 and mark the new time 3:10. Make bigger jumps for bigger increments of time.
- After you have subtracted the time allotted for all of the necessary activities, one by one, you will land on a spot at the timeline that indicates when you should start the process of getting ready to go.
Guided practise(10 minutes)
- Write the following problem on the board: If Jennifer needs to be at her video game tournament at 1:45 and it takes 3 1/2 hours to get there, when should she leave?
- Have students talk to a neighbour about the strategy they would use to solve this problem.
- Share strategies. Have students demonstrate how they would solve the problem.
- Now, you show them how to solve on an open number line if this hasn’t been discussed.
- Make up a word problem as a class, taking student suggestions for the character’s name and what they are doing in the problem. Then have students solve the problem independently or in pairs.
- Circle the parts of this word problem. Name of the person, the arrival time, and the time required for each activity prior to getting there.
Independent working time(20 minutes)
- Instruct students to write their own word problem. Each problem should involve a character, an event, the desired arrival time, and two things that the character in the problem must do before arrival. All times should be in five or ten minute intervals. The question students must solve is: In order to get there in time, when should they start getting ready?
- Have them turn their paper over and solve their own problem. They should draw and label a model that shows what strategy they used to solve it.
- Instruct students to share their problem with a neighbour to see if it has all of the parts.
- Instruct students to put their name on the back of their paper and turn their paper in.
- Redistribute the problems to the class and have students work the problem that they received, drawing and labeling their work.
- Use easier scenarios with times that are in 15 minute, 30 minute, or one hour increments.
- Have students calculate and create problems to the minute.
- Select one of your student’s problems and project it so that they can see only the word problem. Have students draw and label their strategy along with their solution. Collect or spot check their work.
Review and closing(5 minutes)
- Ask your students, "Will this kind of planning always get you there on time?"
- Discuss the kinds of things that could derail your planning (traffic, you forgot something and have to go back, etc.). Ask, "Is there any way to plan for these kinds of unexpected events?" Students may suggest adding in more time as a buffer.