EL Support Lesson
Subtraction Story Problems
Students will be able to subtract within 20 to solve for an unknown part.
Students will be able to describe steps to solve subtraction story problems using manipulatives, pictures and partner support.
- Tell students the story problem, "Kristi had eight pennies. Kristi's friend gave her some more pennies. Now Kristi has 12 pennies! How many pennies did her friend give her?"
- Seat the students in a circle on the rug, or show them pennies on a document camera. Ask students how much a penny is worth. (One cent!)
- Think aloud as you model the problem. Say, "I know that Kristi had eight pennies." Chorally count one penny at a time to show eight. "I want to know how many pennies Kristi's friend gave her. I know she ended with twelve."
- Count on as you create a second pile of pennies, "Nine, ten, eleven, twelve. How many pennies are in this part? How many more did I need to make twelve total?" (Four.)
- Reflect, "That's right! Kristi's friend gave her four pennies!"
Explicit Instruction/Teacher modeling(10 minutes)
- Ask students if there would be a way to show how many pennies Kristi's friend gave her using an equation, or number sentence.
- Think aloud, "Kristi started with some pennies. There were eight pennies in that part. We did not know how many pennies were in the other part. That part was unknown."
- Write 8 + ? on the board, and say, "I will use the question mark because we did not know how many were in that part." Tell students to shrug their shoulders as if asking a question and repeat, "Question mark."
- Say, "We know she ended with 12 total pennies." Finish the equation 8 + ? = 12.
- Remind students that you solved the problem by using pennies and counting on. Tell students to turn and talk to a partner to share other ideas for ways to solve the problem. Display the sentence frame, "I could solve the problem by ____."
- Choose volunteers to share ideas. Guide students in understanding that since 12 is the total number of pennies, 12 - 8 = ? could be used to solve the problem with subtraction.
- Tell students, "Since I know the total number of pennies and one part, I can solve for the unknown part using subtraction. Then, I can use addition to check my answer. This is another way to show that Kristi's friend gave her 4 pennies.**
Guided Practice(5 minutes)
- Tell students that they will work with a partner to solve story problems. Students can choose to use objects, draw pictures or write equations to solve the problems.
- Instruct students to read each problem three times. Create a chart to describe the steps for solving the word problems:
- Read the problem and think about what is happening (sketch a stick figure with a thought bubble)
- Read the problem again, and underline important words in the problem (write common math terms such as more, less, and all together and underline them)
- Read the problem again, and solve the problem. Show your thinking! (write 8 + ? = 12, 12- 8 = ?, draw a picture of the problem, write the solution: 4 pennies)
- Distribute the Subtraction Story Problems worksheet, and model solving the first problem following the steps as you read the problem three times with a different focus for each read.
Group work time(10 minutes)
- Students will work with a partner to follow the steps and solve the word problems. Partners should take turns reading each problem a total of three times.
- Encourage students to explain their thinking as they solve each problem.
- Require that partnerships agree on a solution before moving on to the next problem.
Additional EL adaptations
- Display a poster with numerals and number names 0-20 for reference.
- If students do not know number names in English, allow them to say the number names in their home language (L1).
- Solve the story problems in a teacher-led small group. Translate the problems to L1 if possible.
- Encourage students to act out the problems to improve comprehension.
- Allow students to write their own "change unknown" subtraction word problems. Students can exchange problems with a partner and solve.
- Circulate as students work on the story problem with their partner. Check for comprehension of the situations presented in the problems. Students may automatically think that addition of two parts is required in word problems that include "more." Encourage students to act out the problems, or model with drawings and manipulatives.
- Prompt students to verbalize the steps to solve a story problem by reading the problem three times.
- If students do not answer the problems correctly, ask them to explain their thinking. Encourage the self-correction of errors rather than rushing to provide the correct answer.
Review and closing(5 minutes)
- Review the solutions for problems from the worksheet as time allows.
- Ask students to explain the context of the problem in their own words, and to justify their answers by explaining their thinking.