In this lesson plan, your learner will practice solving First Then Now subtraction stories. We will introduce the story problems with concrete objects and pictures and then represent them with equations.
Here are a few concepts that are helpful to know for this lesson. We'll discuss a few of the different kinds of story problems.
Part-Part-Whole Subtraction: Part-part-whole problems involve a whole quantity that is composed of two or more parts. Subtraction can be used to find the unknown part when the other parts and the whole are known. For example: In a bag of apples, there are 8 red apples and some green apples. If there are 12 apples in total, how many green apples are there? (12 - 8 = ?)
First-Then-Now Subtraction: First-then-now story problems involve actions where something is taken away or removed from an initial quantity. These problems typically follow a sequence of events: first, there is an initial situation, then an action is performed (such as taking away or separating), and finally, the result or remaining quantity is described. For example: There are 10 pencils on the desk. If 4 pencils are taken away, how many pencils are left? (10 - 4 = ?)
First-Then-Now Addition: In addition to subtraction, the first-then-now structure can also be used to solve joining (addition) problems. These problems involve combining or bringing together two or more quantities to find the total. For example: There are 5 apples in a basket. Then 3 more apples are added to the basket. How many apples are there in total? (5 + 3 = ?)
Parts of a Subtraction Equation
It is also helpful to know the names of each part of a subtraction equation:
Minuend: The minuend is the total or the whole quantity from which another quantity (the subtrahend) is to be subtracted. It is the starting or initial amount. Example: In the subtraction equation 10 - 4 = 6, the minuend is 10.
Subtrahend: The subtrahend is the quantity that is to be subtracted or taken away from the minuend. It represents the amount that is removed or taken away. Example: In the subtraction equation 10 - 4 = 6, the subtrahend is 4.
Difference: The difference is the result of subtracting the subtrahend from the minuend. It represents the remaining or resulting quantity after the subtraction. Example: In the subtraction equation 10 - 4 = 6, the difference is 6, which is the quantity left after subtracting 4 from 10.
Teaching Plan
The following activities will help your learner become confident in solving first-then-now subtraction problems. Be sure to work at a pace that is comfortable for your learner.
Examples and visuals to support the lesson:
1. Introducing First Then Now Subtraction Stories
To introduce subtraction story problems with the first-then-now structure, we will start by using concrete objects or pictures. Here's how you can do it:
Begin with a simple story problem like "First, there were five children sitting at the table. Then two children left. Now, there are three children sitting at the table."
Provide pictures or concrete objects with the story problem. Encourage your learner to act out the story using the pictures or objects.
Emphasize the value by which the element is decreased. Using the example of children sitting at the table, place emphasis on the two children who left the table.
Be sure to include contexts that involve the number zero. Use examples such as:
"First, there were three children in the boat. Then, no children got out of the boat. Now, there are three children in the boat." In this example, the subtrahend is 0 because there is no decrease. The equation becomes 3 - 0 = 3.
"First, there were three children in the boat. Then three children got out of the boat. Now, there are no children in the boat." In this scenario, the subtrahend is equal to the minuend (they are both 3) resulting in a difference of 0. The equation can be written as 3 - 3 = 0.
Skill Check
I can act out first-then-now story problems.
2. Transitioning to Abstract Representations
Next, transition to representing the story problems with abstract representations.
Provide your learner with a first-then-now mat and counters. Guide them in moving the counters from one box to the next demonstrating each step of the story problem. You can also incorporate tens frames, bar models, bead string, or number lines to model the steps of the story.
Have your learner fill in the numbers to create a subtraction equation. Guide your learner in making connections between the story and the equation.
For the example of children sitting at a table, you can write 5 - 2 = 3. Then ask your learner, "What does the 5 represent? What does the -2 represent? What does the 3 represent? Encourage them to answer in complete sentences such as: "The -2 represents the children that left the table." Remind your learner that the subtraction symbol represents a decrease.
Discuss the importance of the order of the minuend and subtrahend. At this point, there is no need to teach them that the larger number must come first or that the commutative property does not apply to subtraction. For now, focus on using the steps of the story problem to help your learner write the numbers in the correct order.
Skill Check
I can write and explain subtraction equations that represent first-then-now story problems.
3. Understanding Addition vs Subtraction
Once your learner is confident with both joining and separating problems, provide them with additional opportunities to strengthen their understanding of addition and subtraction.
Present your learner with a story along with a list of addition and subtraction equations. Have them select the equation that represents the story.
Next, provide your learner with an equation and a list of stories. Have them choose the story that matches the equation.
Encourage your learner to justify their answers and explain why the other choices were incorrect.
Skill Check
I can tell if a first-then-now story represents addition or subtraction. I can match first-then-now story problems with equations.
By incorporating concrete objects, visual aids, and relatable story contexts, your learner will gain a solid foundation in understanding subtraction story problems using the first-then-now structure. Transitioning from concrete to abstract representations helps reinforce the concept of subtraction, leading to improved problem-solving skills and a deeper understanding of mathematical operations. Through practice and engagement with various scenarios, your learner will build confidence and proficiency in solving story problems and writing equations.
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Skill Check