standard_description: Compute unit rates associated with ratios of fractions, including ratios of lengths, areas and other quantities measured in like or different units. For example, if a person walks 1/2 mile in each 1/4 hour, compute the unit rate as the complex fraction 1/2/1/4 miles per hour, equivalently 2 miles per hour.
problem_activity: Activity
In this activity, students are building skills that will help them in mathematical modeling (MP4). Students formulate a model by designing a ramp that they think will be accessible. Then they validate their results by comparing them to the Americans with Disabilities Act (ADA) guidelines. Students then use measurement and computation to determine if their ramp is acceptable and redesign it if necessary.
Monitor for the methods students choose to validate their design:
Use the angle to check their ramps by measuring the angle with a protractor.
Use the slope information by measuring to make sure that for every inch of vertical length, there are 12 inches of horizontal length.
Construct one or more slope triangles along their ramp to demonstrate that it meets the guidelines.
Making dynamic geometry software available gives students an opportunity to choose appropriate tools strategically (MP5).
Launch
You may want to do an image search for “bad wheelchair ramp” to show some examples that are not safe to help students come up with good characteristics.
Arrange students in groups. After students make their design, distribute one copy of the ADA guidelines, cut from the blackline master, per group.
Engagement: Develop Effort and Persistence.
Encourage and support opportunities for peer interactions. Prior to the whole-class discussion, invite students to share their work with a partner. Display sentence frames to support student conversation such as: “First, I _____ because . . .”, “I noticed _____ so I . . .”, “Why did you . . .?”, “How did you get. . .?”
Supports accessibility for: Language; Social-emotional skills
Student Facing
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Some buildings offer ramps in addition to stairs so people in wheelchairs have access to the building. What characteristics make a ramp safe?
A school has 4 steps to the front door. Each step is 7 inches tall. Design a ramp for the school.
Your teacher will give you the Americans with Disabilities Act (ADA) guidelines. Does your design follow the rules of this law? If not, draw a new design that does.
Student Response
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Student Facing
Are you ready for more?
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A ramp with a length to height ratio of
\(12:1\)
forms a right triangle with a 4.8 degree angle.
What is the angle measurement if the base is only 6 units long and the height is 1 unit tall?
When the length is half as long does that make the angle half as big?
What is the angle measurement if the base is 6 units long and the height is increased to 2 units tall?
When the height is twice as tall does that make the angle twice as big?
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Extension Student Response.
Anticipated Misconceptions
Some students may be struggling to design a ramp. Ask them what shape is a good model for the side view of a ramp. (A right triangle.)
Activity Synthesis
The goal of this discussion is to see that having a 4.8 degree angle and a ratio of vertical to horizontal length of
\(1:12\)
are equivalent.
Display previously selected drawings of student ramp designs. Tell students, “Simplified diagrams of right triangles are a mathematical model of the cross section of a ramp.” This previews the work with cross sections that students will do in a subsequent unit but there’s no need to define cross section now.
Invite students who used the ratio of
\(1:12\)
to check their ramps to share their process. Make sure that all students understand how to use the ratio to generate the horizontal length of the ramp given the vertical length, as students will need to do this in the cool-down.
Next, invite students who used the angle of 4.8 degrees to share.
Ask students to confirm that ramps in which students checked for a ratio of
\(1:12\)
also have an angle of 4.8, and vice versa. Students should end convinced that having a 4.8 degree angle and a ratio of vertical to horizontal length of
\(1:12\)
are equivalent. In the lesson synthesis, they will connect this concept to triangle similarity.
Representing, Conversing: MLR7 Compare and Connect.
Use this routine to prepare students for the whole-class discussion. At the appropriate time, invite students to create a visual display that includes their ramp design and a justification for whether it meets ADA guidelines. Invite students to quietly circulate and read at least 2 other displays in the room. Next, ask students to find a new partner to discuss what is the same and what is different about the different methods groups chose to validate their designs. Listen for and amplify observations that include mathematical language and reasoning about angles and ratios of side lengths.
Design Principle(s): Cultivate conversation; Optimize output (for justification)


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