Using Geometry to Solve Design Problems

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Geometry › Using Geometry to Solve Design Problems

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1

A garden path is a rectangle $12\text{ ft}$ long and $8\text{ ft}$ wide. A rectangular flower bed must be placed inside it so that there is a uniform border of $1\text{ ft}$ of path on all sides. The flower bed’s side lengths must be whole numbers of feet.

Which design satisfies all constraints?

Bed $11\text{ ft} \times 6\text{ ft}$

Bed $12\text{ ft} \times 6\text{ ft}$

Bed $10\text{ ft} \times 6\text{ ft}$

Bed $10\text{ ft} \times 7\text{ ft}$

Explanation

The skill of using geometry to solve design problems involves applying geometric principles to place features within areas with border requirements. In this case, the path is 12 ft by 8 ft, requiring a 1 ft uniform border on all sides, with whole-foot bed sizes. Geometry applies by subtracting twice the border from each path dimension for maximum bed sizes. Evaluating design options, we verify fits within 10 ft by 6 ft limits. Option A, 10 ft by 6 ft, justifies as the correct choice because it matches the maxima while maintaining borders. A common distractor misconception is subtracting border from only one side, allowing oversized choices like B. To transfer this strategy, check every constraint systematically by computing adjusted dimensions.

2

A rectangular poster is to be centered on a wall section that is $14\text{ ft}$ wide and $10\text{ ft}$ tall. A border of at least $2\text{ ft}$ must remain between the poster and each edge of the wall section. The poster must have perimeter at least $28\text{ ft}$.

Which design satisfies all constraints?

A poster that is $11\text{ ft}\times 6\text{ ft}$.

A poster that is $10\text{ ft}\times 6\text{ ft}$.

A poster that is $9\text{ ft}\times 7\text{ ft}$.

A poster that is $8\text{ ft}\times 5\text{ ft}$.

Explanation

Using geometry to solve design problems involves centering rectangles within larger spaces with border requirements and perimeter minimums. Constraints include a 14 ft by 10 ft wall with at least 2 ft borders on all sides, reducing available space to 10 ft by 6 ft, and perimeter at least 28 ft. Geometry applies by subtracting twice the border from each dimension to determine maximum poster size. Options are evaluated by checking fit within reduced dimensions and perimeter calculation. The 10 ft by 6 ft poster is justified as it fits exactly and has perimeter 32 ft, exceeding 28 ft. A misconception is calculating border only on two sides, allowing oversized options like 11 ft by 6 ft. For transfer, systematically verify every constraint by computing effective dimensions and perimeter values.

3

A small museum is installing a rectangular display case inside a rectangular alcove that is $9\text{ ft}$ wide and $6\text{ ft}$ deep. Building code requires a clear walkway of at least $1\text{ ft}$ along each wall of the alcove (left, right, top, and bottom). Which design satisfies all constraints?

Case $7\text{ ft} \times 4\text{ ft}$, centered in the alcove.

Case $8\text{ ft} \times 4\text{ ft}$, centered in the alcove.

Case $8\text{ ft} \times 5\text{ ft}$, centered in the alcove.

Case $7\text{ ft} \times 5\text{ ft}$, centered in the alcove.

Explanation

This problem requires using geometry to design a display case that fits within spatial constraints. The alcove is 9 ft wide by 6 ft deep, and we need 1 ft clearance along each wall. To find the maximum case dimensions, subtract 2 ft from each alcove dimension (1 ft clearance on each side): width = 9 - 2 = 7 ft, depth = 6 - 2 = 4 ft. Option A (7 ft × 4 ft) exactly meets these maximum dimensions while satisfying all clearance requirements. Option B violates the width constraint (8 ft is too wide), while options C and D violate the depth constraint (5 ft is too deep). A common mistake is subtracting only 1 ft total instead of 1 ft from each side. When solving design problems with clearance requirements, always account for clearance on all sides by subtracting twice the clearance distance from each dimension.

4

A company is cutting a circular logo (radius 5 cm) from a square sticker sheet. The logo must fit entirely inside the square, and the square’s side length must be an integer number of centimeters to match a cutting template. Which square side length best meets the geometric requirements?​

11 cm

10 cm

9 cm

12 cm

Explanation

This problem involves using geometry to determine the minimum square size to contain a circular logo. The constraint is that a circle of radius 5 cm must fit entirely inside a square with integer side length. For a circle to fit inside a square, the square's side must be at least as long as the circle's diameter. The diameter is 2(5) = 10 cm, so the square needs side length at least 10 cm. Since we need an integer value and 10 cm exactly fits the requirement, option B (10 cm) is correct. Option A (9 cm) is too small to contain the 10 cm diameter circle. Options C and D are larger than necessary but would work; however, the problem asks for the size that "best meets" the requirements, implying the minimum sufficient size. The strategy is to identify the minimum geometric requirement (diameter ≤ side) and apply it directly.

5

A community center is installing a rectangular stage on a rectangular floor area that is $24\text{ ft}$ wide and $18\text{ ft}$ deep. Building code requires a clear walkway of at least $3\text{ ft}$ on all four sides of the stage. The stage must be a rectangle with side lengths that are whole numbers of feet.

Which design satisfies all constraints?

Stage $21\text{ ft} \times 12\text{ ft}$

Stage $18\text{ ft} \times 12\text{ ft}$

Stage $19\text{ ft} \times 13\text{ ft}$

Stage $20\text{ ft} \times 12\text{ ft}$

Explanation

The skill of using geometry to solve design problems involves applying geometric principles to fit shapes within spatial constraints while meeting regulatory requirements. In this case, the floor measures 24 ft wide by 18 ft deep, requiring at least 3 ft walkways on all four sides, with stage sides in whole feet. Geometry applies by subtracting twice the walkway width from each floor dimension to determine maximum stage sizes. Evaluating design options, we check if each fits within 18 ft by 12 ft maxima. Option B, 18 ft by 12 ft, justifies as the correct choice because it meets the dimensional limits exactly without violating walkway rules. A common distractor misconception is forgetting to account for walkways on both sides of each dimension, leading to oversized choices like A. To transfer this strategy, check every constraint systematically by calculating allowable dimensions beforehand.

6

A maker is cutting a circular tabletop from a square sheet of wood that is $48\text{ in}$ on each side. The circle must fit entirely inside the square, and the maker also needs a $2\text{ in}$ safety margin between the circle and each edge of the sheet. Which option best meets the geometric requirements?

Tabletop diameter $44\text{ in}$.

Tabletop diameter $46\text{ in}$.

Tabletop diameter $45\text{ in}$.

Tabletop diameter $48\text{ in}$.

Explanation

This problem requires inscribing a circle within a square while maintaining safety margins. The square sheet is 48 in × 48 in with a 2 in margin required from each edge. The available space for the circle is a 44 in × 44 in square (after subtracting 2 in from each side). The maximum diameter for a circle inscribed in this reduced square is 44 in. Option A (diameter 44 in) exactly meets this constraint. Options B (46 in) and C (48 in) would violate the safety margin by extending too close to the sheet edges. Option D (45 in) also exceeds the 44 in limit. A common error is subtracting the margin only once instead of from both sides, leading to an overestimate of available space. When working with safety margins, always account for the margin on all sides by subtracting twice the margin distance from each dimension.

7

A rectangular poster is to be centered on a wall section shown as a 14 ft by 8 ft rectangle. A 1 ft-wide border of empty space is required on all four sides between the poster and the wall edges. Which poster size satisfies all constraints?

$11\text{ ft} \times 7\text{ ft}$

$12\text{ ft} \times 7\text{ ft}$

$13\text{ ft} \times 6\text{ ft}$

$12\text{ ft} \times 6\text{ ft}$

Explanation

This problem involves using geometry to center a poster on a wall with border constraints. The wall is 14 ft × 8 ft, and a 1 ft border is required on all sides between poster and wall edges. This means the poster must fit within a (14-2) × (8-2) = 12 × 6 ft region to maintain 1 ft clearance on each side. Option A (12 × 6 ft) exactly fills this available space while maintaining the required borders. Option B (13 × 6) is too wide by 1 ft, option C (12 × 7) is too tall by 1 ft, and option D (11 × 7) is also too tall. The key insight is that with a uniform border of width b on all sides, the available space is reduced by 2b in each dimension. Always account for borders on both sides when calculating available space.

8

A civil engineer is designing a concrete ramp that must rise 4 feet vertically over a horizontal distance that can vary. Building codes require that the ramp's slope not exceed 1:12 (rise:run), and the ramp's surface must not exceed 80 feet in length due to safety regulations. If concrete costs $8 per square foot of ramp surface, what is the minimum cost to build this ramp if it is 6 feet wide?

$2,304, using the minimum horizontal distance allowed by the slope requirement

$3,840, using the maximum ramp surface length to minimize slope steepness

$1,920, utilizing the most direct path while satisfying the slope constraint

$2,880, balancing the slope and length constraints for optimal cost efficiency

Explanation

The ramp must rise 4 feet. With a maximum slope of 1:12, the minimum horizontal distance is 4 × 12 = 48 feet. The ramp surface length is √(4² + 48²) = √(16 + 2304) = √2320 ≈ 48.17 feet. Since 48.17 < 80 feet, the slope constraint is more restrictive than the length constraint. The ramp surface area is 48.17 × 6 = 289 square feet. Cost = 289 × $8 = $2,312 ≈ $2,304. This is the minimum cost because any steeper slope would violate the code, and any longer horizontal distance would only increase the ramp surface area and cost.

9

A city is painting a rectangular crosswalk inside a road lane. The lane is $11\text{ ft}$ wide. Regulations require a clearance margin of at least $0.5\text{ ft}$ from each edge of the lane to the painted crosswalk (so the crosswalk width must be at most $10\text{ ft}$). The crosswalk width must be a whole number of feet.

Which option best meets the geometric requirements?

Crosswalk width $11\text{ ft}$

Crosswalk width $9\text{ ft}$

Crosswalk width $10.5\text{ ft}$

Crosswalk width $10\text{ ft}$

Explanation

The skill of using geometry to solve design problems involves applying geometric principles to fit features within lanes with margins. In this case, the lane is 11 ft wide, requiring at least 0.5 ft clearance on each side, with whole-foot widths. Geometry applies by subtracting total clearance to find maximum width of 10 ft. Evaluating design options, we identify those meeting the limit and whole-number rule. Option B, 10 ft, justifies as the correct choice because it maximizes width without violating clearances. A common distractor misconception is ignoring clearances, selecting oversized like C. To transfer this strategy, check every constraint systematically by deducting margins first.

10

A rectangular display board must fit entirely inside a right-triangular alcove with legs 12 ft (along the floor) and 9 ft (along the wall). The board must be mounted with one corner at the right-angle corner of the alcove, with its sides parallel to the floor and wall. For safety clearance, the board’s top-right corner must lie on or below the slanted wall. Which board size satisfies all constraints?

$10\text{ ft} \times 4\text{ ft}$

$9\text{ ft} \times 4\text{ ft}$

$8\text{ ft} \times 3\text{ ft}$

$12\text{ ft} \times 2\text{ ft}$

Explanation

This problem requires using geometry to design a rectangular board that fits in a triangular alcove. The constraints are: the board must fit entirely inside a right triangle with legs 12 ft and 9 ft, one corner must be at the right angle, sides must be parallel to the legs, and the opposite corner must not exceed the hypotenuse. The hypotenuse of the alcove has equation x/12 + y/9 = 1, or 3x + 4y = 36. For a board with dimensions w × h placed at the origin, the top-right corner is at (w, h), which must satisfy 3w + 4h ≤ 36. Checking option B (8 ft × 3 ft): 3(8) + 4(3) = 24 + 12 = 36, which exactly meets the constraint. Option A (10 × 4) gives 3(10) + 4(4) = 46 > 36, violating the constraint. The key strategy is to check that all corners of the rectangle satisfy the geometric boundaries.

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