Emma is making a scale drawing of her farm using the scale 1 cm to 2.5 feet. In the drawing, she drew a well with a diameter of 0.5 cm. What is closest to the actual circumference of the well? A. 1 foot B. 2 feet C. 4 feet D. 5 feet
The correct answer and explanation is:
To find the actual circumference of the well, we need to use two key steps:
Step 1: Convert the drawing measurement to real-life size
Emma used a scale of 1 cm = 2.5 feet.
She drew the diameter of the well as 0.5 cm in the drawing.
So, the actual diameter of the well is: Actual Diameter=0.5 cm×2.5 feet/cm=1.25 feet\text{Actual Diameter} = 0.5 \text{ cm} \times 2.5 \text{ feet/cm} = 1.25 \text{ feet}
Step 2: Use the formula for circumference
The circumference of a circle is calculated using the formula: Circumference=π×diameter\text{Circumference} = \pi \times \text{diameter}
Substitute the actual diameter into the formula: Circumference=π×1.25≈3.14×1.25=3.925 feet\text{Circumference} = \pi \times 1.25 \approx 3.14 \times 1.25 = 3.925 \text{ feet}
Step 3: Round to the closest option
The closest value to 3.925 feet among the given choices is:
- A. 1 foot
- B. 2 feet
- C. 4 feet
- D. 5 feet
The correct answer is:
✅ C. 4 feet
Explanation (300 words)
In this problem, Emma is working with a scale drawing where 1 centimeter in the drawing represents 2.5 feet in real life. This type of scale is commonly used in blueprints, maps, and models to represent large areas or objects on a smaller and more manageable scale.
She draws a well with a diameter of 0.5 cm. Since the drawing is scaled down, we need to convert this 0.5 cm measurement to the actual size using the given scale. By multiplying the drawing measurement by the scale (0.5 × 2.5), we find the real-life diameter is 1.25 feet.
Next, to find the circumference—the distance around the circular well—we apply the circle formula: Circumference=π×diameter\text{Circumference} = \pi \times \text{diameter}
Using π ≈ 3.14, and plugging in 1.25 feet for the diameter, we get: Circumference≈3.14×1.25=3.925 feet\text{Circumference} ≈ 3.14 \times 1.25 = 3.925 \text{ feet}
Finally, we compare this value to the answer choices. 3.925 feet is very close to 4 feet, so C is the best answer. The other options are too far from the actual value and do not accurately represent the real circumference.
This problem tests your ability to apply scale factors and geometry formulas, two key skills in both math and real-world problem-solving like construction, design, and architecture.