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A recommendation for wheelchair ramps is that the rise-to-run ratio be no greater than 1:12. This ensures that the ramps are navigable by people in wheelchairs. If a business needs to install a concrete ramp to the entrance of their building, which is 12 inches off the ground, how long should the ramp be and how far out horizontally on the ground will it protrude from the building? Give answers in feet and inches, such as 5 feet, 4 inches. What percent grade is the ramp?

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Answer:

a. 12 feet b. 12 feet 0.5 inches c. 8.33 %

Step-by-step explanation:

a. How far out horizontally on the ground will it protrude from the building?

Since the rise to run ratio is 1:12 and the building is 12 inches off the ground, let x be the horizontal distance the ramp protrudes.

So, by ratios rise/run = 1/12 = 12/x

1/12 = 12/x

x = 12 × 12

x = 144 inches

Since 12 inches = 1 foot, 144 inches = 144 × 1 inch = 144 × 1 foot/12 inches = 12 feet

b. How long should the ramp be?

The length of the ramp, L is gotten from Pythagoras' theorem since the ramp is a right-angled triangle with sides 12 inches and 144 inches respectively.

So, L = √(12² + 144²)

= √[12² + (12² × 12²)]

= 12√(1 + 144)

= 12√145

= 12 × 12.042

= 144.5 inches

Since 12 inches = 1 foot, 144.5 inches = 144 × 1 inch + 0.5 inches = 144 × 1 foot/12 inches + 0.5 inches = 12 feet 0.5 inches

c. What percent grade is the ramp?

The percentage grade of the ramp = rise/run × 100 %

= 12 inches/144 inches × 100 %

= 1/12 × 100 %

= 0.0833 × 100 %

= 8.33 %

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